
■' ,'Uf.l j < i.' 














Manufacture of Cement 


RICHARD bC MEADE 


ff 

CONSULTING CHEMICAL ENGINEER 



MANUFACTURE OF CEMENT 
Parts 1-2 


386 

Published by 

INTERNATIONAL TEXTBOOK COMPANY 


SCRANTON, PA. 


TFS77 

-Ht 


Manufacture of Cement, Parts 1 and 2: Copyright, 1922, 1909, 1902, by Interna¬ 
tional Textbook Company. 


Copyright in Great Britain 


All rights reserved 


Printed 'in U. S. A. 

* i 



International Textbook Press 
Scranton, Pa. 


78957 





CONTENTS 


Note.—T his book is made up of separate parts, or sections, as indicated by 
their titles, and the page numbers of each usually begin with 1. In this list of 
contents the titles of the parts are given in the order in which they appear in 
tne book, and under each title is a full synopsis of the subjects treated. 


MANUFACTURE OF CEMENT, PART 1 


Pages 


Mortar Materials . 1- 4 

Relation between Portland cement and other mortar 
materials; Limes, cements, and plasters. 

Limes and Plasters. 5-31 

Common limes ; Composition of raw materials; Hydraulic 
limes; Plasters. 

Cements .'.. 32-73 


V Natural, Roman, and Rosendale cements; Composition 
and processes of manufacture; Pozzulan cements; 

Portland cement; Raw materials for Portland cement; 
Calculating Portland-cement mixtures; Quarrying of 
dry materials; Mixing processes; Grinding; Varieties 
of mills. 

Burning - Process and Apparatus. 73-86 

Burning the mixture; Rotary kiln; Fuel; Chemical 
changes during burning; Degree of burning; Waste 
heat recovery; Dust from cement kilns; Potash recov¬ 
ery; Cooling the clinker; Grinding the clinker; Storage 
of cement; Packing cement; Power plant. 






IV 


CONTENTS 


MANUFACTURE OF CEMENT, PART 2 


Testing of Portland Cement. 

Physical tests; Specific gravity; Detection of adultera¬ 
tion; Specific gravity test; Fineness; Importance of fine 
grinding; Sieve test; Mixing cement pastes and mor¬ 
tars; Normal consistency; Setting time; Gilmore’s 
needles; Ball test; Addition of retarders to cement; 

Tensile strength; Standard sand for briquettes; Form 
of briquette; Molding of briquettes ; Breaking the bri¬ 
quettes; Briquette tanks; Briquette-testing machines; 
Soundness, or constancy of volume; Causes of unsound¬ 
ness ; Curing of unsound cement. 

Correcting Faulty Portland Cement. 24—25 

Chemical Analysis of Portland Cement and Raw 


Materials . 25-28 

Analysis of Portland cement; Determination of composi¬ 
tion; Analyzing and prospecting the raw materials; 
Calculating the amount of material available; Methods 
of analysis; Analysis of cement mixtures, slurry, etc. 

Inspection of Cement. 39-40 

Chemical Supervision of the Process of Manufactur¬ 
ing Portland Cement. 40-41 

Analysis and Testing of Lime. 42-44 

Analysis and Tests of Plaster. 45 


Pages 

1-24 









MANUFACTURE OF CEMENT 

Serial 2051A (PART 1) Edition 1 


MORTAR MATERIALS 


GENERAL CLASSIFICATION 

1. Relation Between Portland Cement and Other 
Mortar Materials. —Mortar materials may be classified 
according to their properties, methods of manufacture, and 
materials from which they are made, as follows: 

1. Common limes are made by burning relatively pure lime¬ 
stone. When mixed with water they slake and show no 
hydraulic properties. 

2. Hydraulic limes are made by burning impure limestone 
at low temperatures. They slake with water, but show 
hydraulic properties. 

3. Natural cements are made by burning impure limestones 
at a low temperature (insufficient to vitrify). They do not 
slake with water but require to be ground in order to convert 
them into a hydraulic cement. 

4. Portland cement is made by heating to incipient vitrifica¬ 
tion an intimate mixture of an argillaceous substance such as 
clay or shale, and calcareous substances, such as limestone or 
marl, in which mixture the percentage of silica, alumina, and 
iron oxide bear to the percentage of lime the ratio of approxi¬ 
mately 1: 2, which vitrified product does not slake with water 
but upon grinding forms an energetic hydraulic cement. 

5. Puzzolan cements are made by incorporating slaked lime 
with finely-ground slag or volcanic ash or by incorporating a 


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2 


MANUFACTURE OF CEMENT, PART 1 


small proportion of Portland cement clinker with suitably 
treated slag and grinding the mixture intimately. 

6 . Plasters are made by heating gypsum sufficiently to drive 
off three-fourths or all of the combined water which it con¬ 
tains and grinding finely the more or less dehydrated residue. 


TABLE I 

MATERIALS, TREATMENT, AND PROPERTIES OF 
LIMES AND CEMENTS 


Classification 

Raw Materials 

Heat Treatment 

Mechanical 

Treatment 

Properties 

1 . Common, 
limes. 

Made from rela¬ 
tively pure 
limestones 

Burned at low 
temperatures 
-600-900° C. 

Slake on addition 
of water to 
burned product 

Not hydraulic 

2. Hydraulic 
limes. 

Made from argil¬ 
laceous or im¬ 
pure limestone 

Burned at low 
temperatures 
—600-900° C. 

Slake on addition 
of water to 
burned product 

Hydraulic 

3. Natural, Ro¬ 
man, or 

Rosendale 
cement 

Made from argil¬ 
laceous or im- 
pure lime¬ 
stone 

Burned at low 
temperatures 
—600-900° C. 

Do not slake on 
addition of 

water, but 
must be 
ground fine 

Hydraulic 

4. Portland 
cement... . 

Made from an 
intimate mix¬ 
ture of argil¬ 
laceous and 
calcareous 
substances in 
proper pro¬ 
portions 

Burned at high 
temperatures 
-600-1,200° 
C. 

Do not slake on 
addition of 

water, but 

must be 
ground fine 

Hydraulic 

5. Slag or puz- 
zolan ce¬ 
ments .... 

Made from mix¬ 
tures of slaked 
lime and blast¬ 
furnace slag or 
volcanic ash 

Not burned 

Do not slake on 
addition of 

water, but 
must be 
ground fine 

Hydraulic 

6. Plasters. 

Made from gyp¬ 
sum 

Burned at from 
165-200° C. 

Do not slake on 
addition of 
water, but 
must be 
ground fine 

Not hydraulic 


The materials, treatment, and properties of the limes and 
cements mentioned in the preceding classification are given in 
Table I. 


2. Historical Development.—The use of lime as a 
building material antedates written history. Both the Egyp- 















































MANUFACTURE OF CEMENT, PART 1 3 

tians and the Romans improved on lime, which hardens in air 
only, by mixing volcanic ash with it. This produced a puzzolan 
cement which would harden under water, and the Romans 
used such cement in many of their engineering works such as 
the aqueduct which supplied Rome with water. The pyramids 
were constructed with a mortar made from plaster of Paris. 
John Smeaton, the engineer who built the Eddystone light¬ 
house, discovered hydraulic lime while searching for some 
hydraulic cement which he could use in the lighthouse. Roman 
cement was probably first made by Joseph Parker in 1796 in 
Kent County, England. 

Joseph Aspdin, a bricklayer of Leeds, England, invented 
Portland cement in 1824 and secured a patent on the process. 
He called his material Portland cement because when it 
hardened it produced a yellowish-gray mass resembling stone 
from the famous quarries of Portland, England. 

Rock suitable for the manufacture of natural cement was 
first discovered in America in 1819 by Canvass White in 
Madison County, New York. The first successful American 
Portland cement plant was built by David O. Saylor at 
Siegfried, Northampton County, Pennsylvania, who employed 
the local argillaceous limestone for this purpose. 

The manufacture of a puzzolan cement from blast-furnace 
slag and slaked lime was first carried out successfully in 
Germany and was begun in the United States in 1896 by the 
Illinois Steel Company. Several other companies also engaged 
in manufacturing slag cement, as it is commonly called, in 
various parts of the United States. None of these now manu¬ 
facture slag cement,'however. 

3. Cement and Lime Industry.— The cement industry 
is one of the great basic industries of the country. Natural 
A cement was at one time extensively manufactured in America, 
but now only a few plants make this material, which is used 
for laying brick and tile; but for concrete, Portland cement 
has entirely displaced both natural and puzzolan cements. ^ 
Hydraulic limes were never made to any extent in this country, 
natural cement taking their place. 


4 


MANUFACTURE OF CEMENT, PART 1 


Portland cement plants are now located in most of the states 
of the Union, as the raw materials are widely distributed. 
These plants have an annual capacity in excess of 100,000,000 
barrels. Lime is made practically all over the United States, 
the annual production being about 3,350,000 tons of quicklime 
and 850,000 tons of hydrate. The manufacture of plaster is 
also an important industry, the production being 2,000,000 tons 
annually. 


LIMES AND PLASTERS 


COMMON LIMES 


COMPOSITION AND MANIPULATION OF RAW MATERIALS 

4. Varieties of Limestone. — Limestone , the raw mate¬ 
rial from which lime is manufactured, is one of the most 
widely distributed rocks and it is found in nearly all countries. 
It usually occurs in stratified beds of considerable extent show¬ 
ing evidences of having been deposited at a time when the 
country was under water. Limestone was formed during all 
geological epochs from the earliest to the present, and some 
such epochs, the Trenton for example, were distinctly lime- 
stqne-forming periods. At a given time, however, limestone 
may have been forming at one point and sandstone or clay at 
another. 

Limestone, according to its physical properties, is known 
under various other names. The term marl is usually applied 
to the loose, granular, non-coherent limestone which was 
deposited in comparatively recent times in existing or extinct 
lakes. This material is now extensively used in the manu¬ 
facture of Portland cement. Marble is limestone that after its 
formation has been subjected to sufficient heat and pressure 
from geological disturbances to make it more or less crystalline. 
Chalk is a soft, fine-grained limestone composed of finely com¬ 
minuted shells. Oolitic limestone resembles a mass of fish roe 
and is made up of small round grains. Calcareous tufas and 





MANUFACTURE OF CEMENT, PART 1 


5 


travertine are limestones deposited by carbonated spring or 
stream waters along their courses. Stalagmites and stalactites 
are the icicle-like forms of limestone usually found in caves, 
the former projecting upwards from the floor and the latter 
hanging downwards from the roof of the cave. They are 
formed by the drip from the roof of water holding carbonate 
of lime in solution. 

5. Chemical Composition of and Impurities in 
Limestone.— Limestone consists technically of more or less 
pure calcium carbonate, CaC0 3 . In its purest crystalline 
state it forms the mineral calcite or calc spar. Calcite con¬ 
tains 56 per cent, of lime and 44 per cent, of carbon dioxide. 
It is found crystallized in the rhombohedral form and when 
cracked usually breaks up into smaller crystals of the same 
form as the large ones. Calcite containing as much as 99.8 per 
cent, of calcium carbonate is sometimes found. Marbles, 
stalactites, etc., are also very pure and sometimes contain as 
much as 99 per cent, of calcium carbonate. Limestone itself 
seldom contains more than 98.5 per cent, of calcium carbonate. 
Limestones containing much magnesia are called dolomitic 
limestones. The mineral dolomite is a double carbonate of 
calcium and magnesia containing when pure 30 per cent, of 
lime, 22 per cent, of mganesia, and 48 per cent, of carbon 
dioxide. 

The principal impurities in limestone are silica, iron, alumina, 
and sulphur. Silica occurs in the free state as sand or com¬ 
bined as silicate of alumina, while alumina occurs only in the 
form of the silicate. Iron may occur as carbonate, oxide, or 
sulphide, and magnesia is generally found as carbonate. 
Sulphur may occur as sulphide of iron or as sulphate of 
calcium or magnesia. 

Calcium oxide and magnesium oxide are the essential 
elements in lime, the other components being considered impuri¬ 
ties. The purer the lime the better it is, and hence the purer 
the limestone the better lime it will make. The blue and gray 
color usually associated with limestone is caused by the pres¬ 
ence of organic matter. This organic matter burns when the 


6 


MANUFACTURE OF CEMENT, PART 1 


limestone is heated and hence the color of the limestone is not 
often any indication of the quality of lime it will produce. 
Some nearly black limestones burn to a white lime. 

G. Burning’ of Limestone. —If limestone or calcium 
carbonate is heated to 800° C. or over, decomposition takes 
place and carbon dioxide, C0 2 , is driven off and calcium 
oxide, CaO, or lime, remains. The reaction that takes place 
may be expressed as follows: 

Limestone, CaC0 3 , H-heat = lime, CaO ,~\~carbon dioxide, C0 2 

As pure limestone contains 56 per cent, of lime, 100 pounds 
of limestone will produce 56 pounds of lime. Ordi¬ 
narily limestone contains some mineral impurities, which are 
not volatile and hence remain in the lime when the limestone 
is burned, so that generally 100 pounds of limestone will pro¬ 
duce more than 56 pounds of lime. In view of the fact that 
approximately 44 per cent, (all the carbon dioxide) of the lime 
is volatile, lime always contains a much higher percentage of 
impurities than the limestone from which it is produced. 

To calculate the quality of lime which will be produced from 
any limestone, it is necessary only to divide the percentage of 
each constituent by 100 less the percentage of carbon dioxide 
(or loss on ignition) and multiply the quotient by 100. If a 
limestone contained 2 per cent, silica and 42 per cent, carbon 
dioxide, the resulting lime would contain [2-r- (100 — 42)] X100 
= 3.45 per cent, silica. 

The heat necessary to decompose calcium carbonate into 
carbon dioxide and lime is equivalent to 1,451 British thermal 
units per pound of lime produced. 

7. Common Lime Kilns.— The process of burning lime¬ 
stone is carried out in lime kilns of various types. The primi¬ 
tive kind is still used by farmers for burning limestone for 
agricultural purposes. It is rudely constructed of stone and 
located on a hillside where the top is readily accessible for 
charging the kiln with limestone and the bottom for drawing 
out the lime. The kiln itself consists merely of a pot-shaped 
structure with stone walls and has a diameter of 8 or 10 feet at 
the top and a height of 15 or 20 feet. In burning, fuel is 


MANUFACTURE OF CEMENT, PART 1 


7 


charged on grate bars at the bottom and over this is piled a 
layer of limestone broken to a convenient size. Other layers 
of fuel and limestone are then put in until the kiln is full. Fire 
is then kindled and allowed to burn until all the fuel is con¬ 
sumed, which requires several days, and after the contents of 
the kiln are sufficiently cool to handle, the burned lime is drawn 
out. This process of burning is wasteful of fuel owing to the 
amount used to heat up the kiln for 
each burning; also, much time is lost 
in loading, heating, and cooling the 
charge. 

8. Continuous Lime Kilns. 

To avoid these objectionable fea¬ 
tures there are now in use what are 
known as continuous kilns, in which 
the limestone and the fuel are 
charged into 'the kiln at the top and 
the burned lime is drawn out at the 
bottom, no cooling of the kiln being 
necessary. Fig. 1 shows a con¬ 
tinuous kiln. It is lined with fire¬ 
brick and often is from 25 to 30 
feet high. Its greatest diameter is 
usually 8 or 10 feet and its diameter at the top and the bottom 
is from 4 to 6 feet. 

The kiln is provided with an arrangement whereby the lime 
may be drawn at regular intervals from below. This type 
of kiln is also built on the side of a hill, usually of lime¬ 
stone blocks, and is often lined with firebrick. In charging 
the kiln, first a layer of small size coke or anthracite coal 
and then a layer of limestone is fed into the top. Fire is 
started at the bottom and works its way up. The process 
of charging and drawing the lime is continuous. These 
kilns are economical of fuel and for the same-sized kiln yield 
a larger quantity of product than do the flame kilns described 
later. On the other hand, the lime is contaminated by the ash 
of the fuel and the lime burned in these kilns must be care- 






















Fig. 2 


8 


























































































MANUFACTURE OF CEMENT, PART 1 


9 


fully sorted in order to discard those lumps to which fuel ash 
has adhered. Many old lime plants are equipped with these 
kilns, but practically all plants aiming to make a high-grade 
building and chemical lime now use flame kilns. Kilns of this 
type are known as mixed-feed kilns because the fuel is mixed 
with the limestone. Mixed-feed kilns are also made similar 
to the flame kiln shown in Fig. 2, except that the fireboxes on 
each side of the shaft are omitted. 

9. Flame Kilns.— When a white lime is required, flame 
kilns are used. As seen from the illustration, the fireplaces a 
are distinct from the body of the kiln. The limestone is 
charged into the main body b, the fuel in the fireplaces is 
kindled, and the hot gases rise up through the limestone into 
the kiln. The finished lime is withdrawn through c. Flame 
kilns are usually from 40 to 50 feet high and from 5 to 8 feet 
inside diameter, and equipped with either two or four furnaces. 
Kilns of this kind are now installed in all the larger lime¬ 
burning plants, as, taking everything into consideration, they 
not only give a more satisfactory product but are easier to 
control and hence more economical. 

In a well-designed flame kiln, the shaft is divided into three 
parts. The upper section, or hopper, unlined with firebrick, 
forms a bin for the storage of stone, so that the kiln may be 
kept supplied at night when the quarry is not working. The 
middle section, or kiln proper, is lined with firebrick and in 
this the stone is burned, the last trace of carbon dioxide being 
driven off as it passes down past the arch or opening connect¬ 
ing the firebox and the shaft. The lower section, or cooling 
cone, is not lined with firebrick and is placed in such a way 
that air can pass around it freely and not only cool the lime 
but also prevent the cone itself from being burned out. The 
bottom of the cone is closed by means of a pair of swinging 
or sliding doors which allow the lime to drop into a barrow 
placed below the cone. 

A kiln 6 feet in diameter by 50 feet high will produce about 
10 tons of lime per day. Most lime plants therefore employ 
several such kilns. They are usually arranged in a row with 


10 


MANUFACTURE OF CEMENT, PART 1 


the fireboxes at right angles to the row, and charged from an 
incline and a cable hoist by means of which the cars of lime¬ 
stone are drawn from the quarry to the top of the kilns. The 
fireboxes rest on a floor usually of steel and concrete which 
extends from 10 to 15 feet beyond the end of the furnace, 
to provide room for the fireman to stoke his fires properly. 
The lime is drawn at intervals of 3 to 6 hours, although a 
few plants draw oftener and some less frequently. The objec¬ 
tion to drawing too frequently is that each time the lime is 
drawn cold air enters the kiln through the drawing doors and 
cools the charge. 

10. Fuel Required to Burn Lime.— Wood, coal, oil, 
natural and producer gas are employed for heating these kilns. 
Wood is the best fuel for burning lime, as wood burns with 
a long flame of comparatively low temperature. This is an 
advantage, as it is essential that the heating should be carried 
for a considerable distance inside the kiln, so as to burn the 
lime completely in the center, without having the temperature 
at the arch or the mouth of the firebox so high that it will fuse 
the lime just in front of it. Wood-burned lime is whiter than 
lime burned with coal. Kilns fired with wood also require less 
attention and skill in operating. Wood, however, is becoming 
scarce in nearly all lime-producing sections and hence it is 
rapidly ceasing to be a fuel for this purpose. 

Where coal is employed this is usually long flame coal, high 
in volatile matter, and preferably low in sulphur and ash. It is 
the usual practice to wet the coal before charging into the 

furnace in order to supply steam and make the coal flame 

* 

resemble more nearly that of wood. A steam jet is also often 
employed, it being inserted under the grate bars. The steam 
passing up through the bed of the hot coals is decomposed and 
forms hydrogen and carbon monoxide according to the reaction 
H 2 0~\~C — CO~\~H 2 . Both of these are combustible gases 
which, passing through the arches, burn in the kiln itself and 
hence carry the heating zone farther into the latter. 

Oil is used for burning lime when it can be obtained more 
cheaply than coal and when atomized with steam it makes a 


MANUFACTURE OF CEMENT, PART 1 


11 


fuel almost as satisfactory as wood. It is used in kilns of the 
type shown in Fig. 2, by placing the oil jet in the door of the 
firebox, after covering the grate bars with firebrick or filling in 
to this point with some suitable material. The door of the fire¬ 
box is partly bricked in with firebrick, leaving openings for 
the jet, for observing the lime, etc. Natural gas has been used 
for burning lime, but the high temperature of its flame is 
objectionable. 

The quantity of fuel required to burn a ton of lime when 
properly used is about as follows: 1 ton of bituminous coal, 

hand fired, will burn 3 to 4 tons of lime; 1 cord of seasoned 
hardwood will burn 2 to 2J tons of lime; 1 barrel of fuel oil 
will burn f to 1 ton of lime. 

11. Producer Gas-Fired Kilns. —Lime kilns are now 
often heated with producer gas, particularly in large plants, as 
one of its principal advantages is the fact that very much larger 
gas-fired kilns can be built than is possible with hand firing on 
a grate. Some gas-fired kilns have a capacity of 40 to 50 tons 
of lime per day. This increased size of the kiln is made 
possible by the introduction of gas and air at various points 
around the kiln so as to obtain uniform temperatures through¬ 
out the stack. Even a kiln of the size described in Art. 10 will 
produce 20 to 25 tons of lime per day when heated with pro¬ 
ducer gas. Producer-gas kilns are slightly more economical of 
both fuel and labor than grate-fired kilns. Unless carefully 
handled, however, the lime obtained is burned very unevenly. 

In Fig. 3 is shown a gas-fired kiln quite similar to the hand- 
fired kiln, the gas ports taking the place of the fireboxes of the 
latter. At d and d are the gas ports. The flow of gas is regu¬ 
lated by means of the valves e, which are counterbalanced by a 
weight. The gas mains leading from the producer are shown 
at /. The top of the kiln is closed by means of a hopper and 
bell g similar to that used with blast furnaces. Draft is secured 
by an exhauster (not shown), the gas being drawn off through 
the flue h. The producers, not shown in the drawing, should 
be located as near the kiln as possible and should be arranged 
so that they can be charged with coal and the ashes removed 


12 manufacture of cement, PART 1 

with the minimum amount of labor. Producers for lime burn¬ 
ing- should give a gas of regular composition which need not, 
however, be of high thermal value. Quite a number of the 



Fig. 3 

standard gas producers have been employed with lime kilns, 
and where properly handled give good results. More skill is 
required m burning lime with producer gas than with any other 
















































































































MANUFACTURE OF CEMENT, PART 1 


13 


fuel. A well-designed gas-fired kiln will require about 1 ton 
of bituminous coal for every 5 to 6 tons of lime burned. 

12. Rotary Kilns for Lime.— The rotary kiln described 
later on is employed to some extent for lime burning, generally 
for lime which is to be used for agricultural, chemical, or metal¬ 
lurgical purposes, or for the manufacture of hydrate, as the 
fine lime produced is not popular in the building trades. For 
this purpose the kiln is heated by producer gas or pulverized 
coal and the limestone is crushed to a 2-inch size and under 
before being put into the kiln. 

The advantages of the rotary kiln are its low labor cost of 
operating and the uniformity with which it burns, if properly 
handled. The labor item of lime burning can be cut in half by 
operating a rotary kiln. The greatest advantage of the rotary 
kiln, however, is the fact that small stone can be burned in it. 
For this reason, a rotary kiln is often used to burn up the lime¬ 
stone chips which are found in all quarries. The rotary kiln 
is also suited for burning stones which break up into smaller 
pieces and crumble on heating. Stone of this type can not be 
burned in upright kilns because of the stopping up of the draft 
by the spalls. 

Certain waste products of manufacturing operations, as, for 
example, the precipitated carbonate of lime from beet-sugar 
manufacture and the lime waste from wood pulp made by the 
soda process, can be successfully burned in only the rotary 
kiln. A rotary kiln 8 feet in diameter by 125 feet long will 
produce daily about 100 tons of lime and will require about 
1 ton of coal to produce 4 to 4£ tons of lime. 

A rotary kiln used for lime does not differ materially from a 
cement kiln except that producer gas is often used to heat the 
lime kiln. Rotary coolers are usually placed after the kiln to 
cool the lime and the stone is fed from a bin into the kiln in a 
regular stream. 

13. Characteristics of Lime. —The lime drawn from 
kilns consists of hard, rock-like, white or light-colored lumps, 
together with more or less fine powder. Lime is highly 
refractory and resists the highest heat of a furnace without 

386—2 


14 


MANUFACTURE OF CEMENT, PART 1 


fusing. Freshly burned lime has a strong affinity for water 
and absorbs considerable moisture from air with a marked evo¬ 
lution of heat. This is due to the chemical union of lime with 
water in forming calcium hydrate,* Ca(OH) 2 , or what is 
known as slaked lime , the reaction being as follows: 

Ca0+H 2 0 = Ca(0H) 2 

The slaking is accompanied by a considerable increase in 
volume as well as weight, since 56 parts of lime combine with 
18 parts of water to form 74 parts of slaked lime, or calcium 
hydrate. Slaking may be accomplished either by exposure to 
moist air or by the addition of water. When mixed with sand 
for use as mortar, slaked lime hardens because of the absorp¬ 
tion of carbon dioxide from the air and the consequent for¬ 
mation of calcium carbonate, which serves to bind together the 
grains of sand. The chemical reaction is as follows: 

Ca(0H) 2 +C0 2 = CaC0 3 +H 2 0 

14. Slaking- of Lime.— All lime, whether used in sand 
mortar for masonry or plaster or almost pure for finishing 
work in plastering, must be perfectly slaked before using. 
Very frequently too little attention is paid to slaking and 
defective work results. The reason is obvious. If lime is 
only partly slaked, it consists of a mixture of quicklime, CaO, 
and calcium hydrate, Ca(OH) 2 , and when mixed with sand 
and put in work, even with excess of water, some quicklime 
may still remain. The water evaporates rapidly and the mass 
may become sound and hard, but it still contains quicklime 
having a strong affinity for moisture, which must be obtained 
from the atmosphere. The process of hydration may prevent 
hardening of mortar to a certain extent, but hardening 
advances as the amount of free lime grows less, and some of 
the lime must become hydrated after the first stage in harden¬ 
ing. As hydration is accompanied by a considerable increase 
in volume, the mass swells or expands and peels or cracks, 
making the work very defective. It is therefore recommended 
that lime be thoroughly slaked for at least a week before being 

*It should be remembered that the word hydrate is the commercial 
term for hydroxide. 



MANUFACTURE OF CEMENT, PART 1 


15 


used, but this practice is not always followed. In some cases 
specifications require even a longer period. 

15. Magnesian Limestones. —Limestones frequently 
contain considerable magnesia. When the magnesian lime¬ 
stones are burned, the resulting lime differs somewhat in prop¬ 
erties from that burned from a purer limestone. Magnesian 
limes slack much slower than do high-calcium limes and 
with evolution of much less heat, and there is no danger of 
burning, but time must be given it to hydrate thoroughly. 
Magnesian limes do not swell quite so much as the high-calcium 
lime when slaked, but shrink less when they harden. 

Magnesian mortars generally work more smoothly and 
spread more freely under the trowel than high-calcium limes. 

TABLE II 

ANALYSES OF BUILDING LIMES 


Percentage of Ingredients in Lime 


ingredients 

1 

2 

3 

4 

5 

Silica, Si0 2 . 

.79 

1.02 

1.38 

.61 

.46 

Iron oxide, F<? 2 0 3 , and 






alumina, AZ 2 0 3 . 

.26 

.68 

.62 

.25 

1.10 

Lime, CaO . 

97.48 

96.46 

97.80 

56.92 

55.49 

Magnesia, MgO . 

1.40 

.64 

.18 

38.09 

42.31 

Carbon dioxide, C0 2 , 






water, H 2 0 , etc. 


1.20 


2.75 

.64 


Hence, magnesian mortars are generally preferred by plas¬ 
terers. The high-calcium limes, on the other hand, give a 
larger volume of putty and carry more sand, so that when 
they can be used they are often cheapest. Magnesian limes 
are generally considered stronger than high-calcium limes. 

16. Composition of Limes. —In Table II are given 
some analyses of lime from various parts of the United States. 
Column 1 gives the composition of lime from Chazy, New 


























16 


MANUFACTURE OF CEMENT, PART 1 


York; column 2 that of lime from Glens Falls, New York; col¬ 
umn 3 that of lime from Bedford, Indiana; while columns 4 
and 5 give the composition of magnesian limes from Sandusky, 
Ohio, and from Sheboygan, Wisconsin. 

17. The impurities in lime all have some influence on its 
properties. The presence of very small amounts of iron tends 
to color the lime red or yellow, while manganese makes it gray 
or black. Silica decreases the plasticity of lime and its sand¬ 
carrying capacity, but alumina on the other hand increases 
these properties. When lime is to be used for building purposes 
it may, contain a somewhat larger amount of impurities than 
when used for plaster finishing and chemical purposes. Many 
limes which contain from 5 per cent, to 10 per cent, impurities 
find extensive local use. Some of the lime sold locally for 
fertilizer is very impure, containing often only 65 per cent, 
of lime. Where lime is shipped any distance, however, it is 
usually quite pure. 

Lime is employed for many purposes besides building. It is 
used for water softening, for purifying coal gas, in tanning 
leather, in the manufacture of sugar, wood-paper pulp, glass, 
calcium carbide, bleaching powder, lye, and other chemicals. 
For most of these purposes a high-calcium lime is required, 
although both kinds are used for fertilizer, and dolomitic lime 
is preferred for wood-pulp manufacture. For all of these 
purposes the value of the lime increases with its purity. 


HYDRATED LIME 

18. Dry ready-slaked lime is sold under the name of 
hydrated lime. The advantages possessed by hydrated lime 
over quicklime are numerous. It is more conveniently handled 
and cheaply shipped, as it is packed in bags. It will keep much 
better, as it does not air-slake. There is no risk of fire due to 
the heat which will be liberated when water accidentally reaches 
quicklime in storage. It is ready for use at all times, being, if 
properly prepared, thoroughly slaked. It can also be con¬ 
veniently mixed with cement, rendering the latter waterproof 
and more plastic. 



MANUFACTURE OF CEMENT, PART 1 


17 


If lime is free from impurities it will take up 32.1 per cent, 
of water. Lime in slaking liberates 485 B. T. U. per pound 



of lime hydrated. This heat is sufficient to evaporate about 
J pound of water, It will be seen, therefore, that if to 1 pound 




































































































































































































18 


MANUFACTURE OF CEMENT, PART 1 


of lime about .8 pound of water is added, about .3 pound of 
this water will enter into combination with the lime and the 
other .5 pound will be evaporated by heat produced by the 
combination of the lime and water, leaving a dry powder con¬ 
sisting of calcium hydrate. In practice some heat is lost in 
radiation, so the amount of water which can be added is some¬ 
what below .8 pound per pound of lime. It usually is not 
greater than .6 pound in the case of high-calcium limes, and in 
the case of magnesian limes is still less, as all of the mag¬ 
nesium oxide is not converted into hydrate. Hydrated lime is 
a fine powder practically all of which will pass a No. 100 test 
sieve. It is packed in burlap or cloth bags holding 100 pounds 
or in paper bags holding 50 pounds. 

19 . Process of Manufacture. —In the process of manu¬ 
facture the quicklime is first crushed to about \ inch and under, 
or even finer. It is then mixed with water just sufficient to 
hydrate all the lime and yet not so much that the heat of slaking 
will not evaporate the excess, when it falls to a dry powder. 
The slaked lime is then ground to break up clots of hydrate, 
and the coarse particles are separated out by means of an air 
separator. 

Fig. 4 shows a hydrated-lime plant. In this the lime is first 
passed through a Sturtevant open-door crusher a. This works 
on the same principle as an ordinary coffee grinder and reduces 
the lime to such a size that it will all pass through a -|-inch 
screen. This is fine enough for hydrating purposes. From 
the crusher the lime is elevated into a large bin b in the top of 
the building. The bottom of the bin is provided with a spout 
and gate, the latter being opened and closed by a lever. Below 
the spout is located a weighing hopper c, and beneath this, the 
hydrator d. The hydrator is a Clyde hydrator. This machine 
is shown in detail in Fig. 5 and consists of a revolving pan a 
provided with plows b, which stir up and mix the water and 
the lime. The pan is revolved by means of a gear c and pinion 
located on the under side of the pan. The pan is covered by 
means of a hood d and a stack f leading through the roof of 
the building. The hood does not revolve. In the center of the 


MANUFACTURE OF CEMENT, PART 1 19 

pan is a metal rim g which closes a circular opening 1 . The 
rim g is raised, exposing the opening, by the wheel h and axle, 
and the hydrate when finished is discharged through this open¬ 
ing. The hydrator rests on the second floor and the scale box, 
valve, and indicator to the water tank are also on this floor, 
so that all the operations of the hydrator are controlled at one 
point. The lime is weighed out in batches of 1,800 to 2,500 



Fig. 5 


pounds and dumped directly from the scale hopper into the 
hydrator. The water is measured in a tank which is beside the 
lime bin. 

The process of hydration consists in first weighing out the 
lime, measuring the water, dumping the lime into the hydrator, 
and then spraying the water on the lime. The lime is usually 





























































































































































20 


MANUFACTURE OF CEMENT, PART 1 


stirred for some time after all the water has run out of the 
tank in order to allow the steam to escape. At first the 
lime is very wet, but as chemical combination takes place it 
dries out and falls to a fine powder, the charge swelling up 
greatly. The whole operation lasts from 15 to 20 minutes. 
When the operator judges the hydration to be complete, the 
lime is dumped into a large bin or hopper e , Fig. 4, by means 
of a valve in the center of the hydrator capable of holding com¬ 
fortably the charge from the hydrator. This hopper is of steel 
and is provided with an automatic feeder at the bottom. This 
feeder serves to regulate the supply of lime going from the 
hydrator to the pulverizer and is so adjusted as to supply the 
pulverizer at the proper rate. The lime usually falls from the 
feeder into a screw conveyer which carries it to the pulverizer. 

20 . After slaking the lime is in the form of a very fine 
fluffy powder mixed with occasional larger pieces, or cores. 
These cores consist of unburned limestone, silicious matter 
which has been partly vitrified, and overburned lime which has 
not been hydrated. The two latter substances, if left in the 
lime, will cause trouble, because when this lime is used for 
plaster they will not slake immediately when mixed with the 
water, but will eventually do so. When lime slakes, expansion 
occurs, and hence wherever there is one of these cores in the 
wall a blister occurs. It is necessary, therefore, either to grind 
these cores so finely that they will hydrate at once when water 
is added to them, or, which is better, to separate them from the 
hydrate. 

For treatment of the lime after passing through the hydrator 
the Raymond system is almost universally employed. This 
system consists of three parts, a pulverizer, a fan, and a 
collector. The lime first goes to the pulverizer located on 
the ground floor. The pulverizer is equipped with an auto¬ 
matic throw-out. This latter separates any cores from the 
hydrate. From the pulverizer the fine product is sucked by 
means of a fan and blown into a dust collector. This col¬ 
lector is located above the packing bin and the hydrate falls 
from the collector into the packing bin. The packing is 


MANUFACTURE OF CEMENT, PART 1 


21 


done by means of Bates packers, and Bates valve bags are 
used. This system will be described later. 

21 . There are several other types of hydrators on the mar¬ 
ket. The Schaffer hydrator consists of a series of pans one 
above the other. Plows revolve in the pans and mix the water 
and the lime. The lime and water are fed into the top pan 
and the hydrate works its way out at the bottom, etc. The 
Kritzer hydrator consists of a number of cylinders one above 
the other which are provided with paddles which revolve 
around a central shaft and stir the lime and water. The lime 
is fed into the top cylinder where the water is added, and the 
hydrate is discharged from the bottom cylinder. Both the 
Schaffer and Kritzer hydrators are continuous while the Clyde 
is a batch machine. 

In place of the Sturtevant mill shown the lime may be 
crushed by means of hammer mills or rolls. If the cores are 
ground with the hydrate, instead of being separated from it, 
the crushing is done by passing the hydrate through a pul¬ 
verizer mill. Tube mills and Fuller mills have been used for 
this purpose. Some of the older mills employ shaking screens 
instead of air separators to remove the cores. 


SAND-LIME BRICKS 

22 . The term sand-lime bricks is applied to bricks that are 
made by mixing sand with a small percentage of slaked lime.' 
The mixture is then pressed into molds and the product 
hardened either by artificial or sun heat. The process is an 
old one that has recently been revived, many patents covering 
various details of the process having been granted during the 
past few years. 

In most modern plants the material used in these bricks 
is clean, usually white, quartz sand free from clay and con¬ 
taining considerable fine material. All the sand should pass a 
20-mesh sieve and at least 10 or 15 per cent, of it should pass a 
100-mesh sieve. The strength of the bricks will in a large 
measure depend on the amount of fine sand in the mixture, the 
weakest bricks containing the largest percentage of very fine 



22 


MANUFACTURE OF CEMENT, PART 1 


sand. In making the bricks the sand is dried and mixed with 
5 to 10 per cent, of slaked lime which should be free from 
oxide of iron in order not to color the bricks, and very care¬ 
fully slaked. Water is then added to the mixture and the 
material pressed into shape in a mold by a pressure of 200 to 
250 tons per brick. The bricks are then loaded on trucks and 
run into a large horizontal cylinder that can be tightly closed. 
Here the bricks are hardened by subjecting them to steam 
under pressure for a period of time depending on the pres¬ 
sure, 6 hours being sufficient to harden the bricks when steam 
at a pressure of 150 pounds is employed. 

Bricks of this kind have a crushing strength of 3,500 to 
5,000 pounds per square inch, but are neither so dense nor so 
strong as good, well-made clay bricks. 


HYDRAULIC LIMES 

23 . The term hydraulic lime is applied to those cementing 
materials which contain sufficient silica and alumina to give 
them hydraulic properties and yet enough free lime to make 
them slake on the addition of water. Compared with Portland 
and natural cements, hydraulic limes are only feebly hydraulic. 
Therefore they are almost unknown in the United States, where 
an abundance of material for the manufacture of cement exists. 
As the cost of manufacturing cement is only a trifle greater 
than that of manufacturing hydraulic lime, and as cement is by 
far the best of the two, it is unlikely that hydraulic limes will 
ever be manufactured to any extent in the United States. In 
France and other parts of Europe, however, the making of 
hydraulic lime is an important industry. The limestones 
used in the manufacture of hydraulic limes usually contain 
between 70 and 85 per cent, of calcium carbonate. The per¬ 
centages of iron and alumina are usually low and rarely exceed 
3 per cent. 

24 . Calcination. —The calcination of hydraulic limes is 
accomplished in shaft kilns similar to mixed-feed lime kilns, 
coal or coke being the fuel commonly used. Before being 



MANUFACTURE OF CEMENT, PART 1 


23 


charged the rock is broken into pieces about the size of the 
head, in order to facilitate burning and to prevent too large an 
amount of undecomposed carbonate. No grinding machinery 
is used either before or after burning, as a good hydraulic lime 
should fall to powder when slaked. The slaking is, of course, 
much slower than with quicklimes. The composition of the 
raw material may also be such that, when calcined at a low 
temperature, it will yield a product whose chemical analysis 
closely resembles that of Portland cement. 

25 . Graphier Cements.— What are known as graphier 
cements are made by grinding finely the lumps of under¬ 
burned and overburned material that remain after a hydraulic 
lime is slaked. Since the underburned portions are merely 

TABLE III 

COMPOSITION OF HYDRAULIC LIMES AND GRAPHIER 

CEMENTS 


Material 

Loss on 
Ignition 
Per Cent. 

Si0 2 

Per 

Cent. 

AhOz 

Per 

Cent. 

FezOz 

Per 

Cent. 

CaO 

Per 

Cent. 

MgO 

Per 

Cent. 

S0 3 

Per 

Cent. 

Hydraulic lime (German) 

5.24 

32.60 

7.17 

6.23 

44.96 

1.52 

1.20 

Hydraulic lime (French) 

8.55 

21.60 

2.00 

1.25 

65.80 

1.35 

.15 

Graphier cement, La- 








farge (French). 

1.28 

31.10 

4.43 

2.15 

58.38 

1.09 

.60 

Graphier cement, 








Mier’s (German).... 

7.93 

23.90 

6.86 


58.49 

1.00 

1.49 


limestone the value of the cement will depend on the rela¬ 
tive proportions of overburned and underburned material 
in the mixture. If nearly all the cement consists of overburned 
material the resulting cement is almost as good as Portland 
cement. Graphier cements contain practically no soluble 
sulphates, and consequently they do not stain masonry. The 
non-staining cements, such as the brand known as Lafarge, 
now imported into the United States, are graphier cements. 

26 . Composition of Hydraulic Limes. —In Table III 
are given the compositions of two foreign non-staining graphier 
cements, and of several hydraulic limes. 























24 


MANUFACTURE OF CEMENT, PART 1 


PLASTERS 

27 . Gypsum.— When pure the mineral gypsum is a 
hydrous sulphate of calcium having the formula CaS0 4 ~\~2H 2 0 
and consisting of 32.6 per cent, of lime, CaO, 46.5 per cent, of 
sulphur trioxide, S0 3 , and 20.9 per cent, of water. As 
quarried, however, gypsum usually contains more or less 
impurities, the chief ones being carbonates of calcium and 
magnesia, silica, oxide of iron, and alumina. Alabaster, which 
is sometimes used for statuary, is a pure white, fine-grained 
gypsum. Anhydrite, CaS0 4 , closely resembles gypsum, but it 
contains no water, hence its name. It cannot be used for the 
manufacture of plaster of Paris or wall plaster. 

Pure gypsum is white and in the crystalline form is trans¬ 
lucent. As quarried or mined, however, gypsum is usually 
opaque and colored from impurities. It has a specific gravity 
of 2.3 and occurs in beds, being frequently found associated 
with rock salt and almost always mixed with beds of limestone 
and red shale. Gypsum deposits were formed under water by 
the gradual evaporation of lakes, etc., whose waters contained 
calcium sulphate. Workable deposits of gypsum in the 
United States were formed chiefly during three geological 
periods, the Silurian, the Lower Carboniferous, and the 
Permian. Large quantities of very pure gypsum are imported 
into the United States from Nova Scotia and New Brunswick. 

28 . Plaster of Paris..— If gypsum is heated to a tem¬ 
perature between 212° and 400° F., 75 per cent, of the water 
of crystallization that it contains will be driven off, and the 
resulting compound known as plaster of Paris will have the 
formula ( CaS0 4 ) 2 H 2 0 and will be composed of 93.8 per cent, 
of calcium sulphate, CaS0 4 , and 6.2 per cent, of water. 

If gypsum is heated to a temperature above 400° F., all 
its water will be driven off and it will become anhydrous 
calcium sulphate, CaS0 4 . Plaster of Paris is manufactured 
on a large scale in the United States, the process consisting 
in grinding the gypsum to a fairly fine powder, calcining this 
powder at a temperature between the limits indicated, and 


MANUFACTURE OF CEMENT, PART 1 25 

then sieving and if necessary regrinding the coarse particles. 
The general steps in the process are shown in Fig. 6. 

As it comes to the plaster mill, the lump gypsum is first 
crushed to a size of 2 to 4 inches by means of a gyratory or 
toggle-joint crusher such as is used for breaking stone for 
ballast and road-making purposes. The product of the 



Fig. 6 


crushers is then sent to the crackers, which work on the same 
principle as an ordinary cofifee mill. The cracker shown in 
Fig. 7 consists of a central shaft a actuated by means of over¬ 
head gears b. This shaft has securely fastened to it two burrs, 
the upper of which, c, has coarse teeth and the lower, d, fine 
corrugations. These two burrs revolve inside of two cone- 


































26 


MANUFACTURE OF CEMENT, PART 1 


shaped receptacles e and /. The upper of these has coarse 
teeth and the lower has corrugations. It will be noted that 
the space between the burrs and the cones gets less as the 
bottom is reached. The material is fed into the upper cone or 
hopper and works its way down and out. These crackers 



reduce the gypsum to pieces about \ inch or smaller. From 
the crackers the materials pass to the fine grinders, which con¬ 
sist of rock-emery mills or sets of burrstones. These reduce 
the gypsum to such a size that from 50 to 75 per cent, of it will 
pass a 100-mesh sieve. After being ground to this fineness 
the gypsum is ready for calcining. 



























































































MANUFACTURE OF CEMENT, PART 1 27 

29 . The calcining of gypsum is usually done in kettles. 
The kettle, shown in Fig. 8, consists of a cylinder a of sheet 
steel 8 or 10 feet in diameter and 6 or 8 feet deep, with a con¬ 
vex bottom of cast iron. This device has two or four hori¬ 
zontal 12-inch flues b, b that are placed about 8 inches from 
the crown of its bottom and about 6 inches apart. It is also 



provided with a top c that has a door d through which the 
ground gypsum is introduced. The kettle is mounted on a 
masonry fireplace e and is partly surrounded by masonry so 
that the products of combustion pass through the flues. As 
the gypsum must be kept continually agitated to prevent 
caking and the burning out of the kettle bottom, the kettle is 































































































28 


MANUFACTURE OF CEMENT, PART 1 


provided with a stirrer. This latter consists of a vertical 
shaft / attached to which are two cross-arms, the one, h, being 
straight and the other, at the bottom, being curved. These 
cross-arms act as the stirrers. Both the kettle and firebox are 
provided with stacks i and j, respectively. The kettles are 
provided with ports or openings g through which the calcined 
gypsum may be discharged. The kettles hold from 7 to 12 
tons of gypsum and from 10 to 25 horsepower is required to 
run the stirrer. The process of calcining requires from 2 to 3 
hours. 

In calcining gypsum the material is fed into the kettle a 
little at a time until it is full, and as the temperature rises to 
about 220° F., the contents of the kettle boils just as water 
does, until the water or moisture that is held mechanically 
is all driven off. The temperature is then raised to about 
300° C., when the chemically combined water begins to come 
off, and at from 350° to 400° C. the process is complete. 
The expelled water is led off by means of a stack set into the 
top of the kettle and the calcined material is run into a fire¬ 
proof pit where it is allowed to cool slightly. It is then 
screened through a revolving separator made of wire cloth, 
and the coarse material is reground by burrstones. 

Burrstones are not very efficient grinding machines and 
modern engineers are gradually replacing them with more 
efficient machines. The burrstones not only take more power 
than other pulverizers but they also do not grind as fine and the 
dressing of the stones themselves requires considerable skill 
and time. In the newer plaster mills the grinding of the 
gypsum is done by means of Raymond roller mills and the 
material is ground to its ultimate degree of fineness before 
being introduced into the kettles. The Raymond roller mill 
requires that the gypsum be dried before being ground and 
this drying is done in rotary driers similar to those used in 
cement mills. The gypsum after being dried is ground to the 
fineness required of the finished plaster, then it is calcined, and 
after cooling it is ready for use. 

The finer the plaster is ground, the better it is. Usually, 
however, it is not ground finer than about 85 per cent, pass- 


TABLE IV 

COMPOSITION OF PLASTER MATERIALS 


MANUFACTURE OF CEMENT, PART 1 


29 


Water, 

H 2 O 

Per Cent, 

20.52 

20.43 

20.94 

6.98 

6.33 

trace 

Carbon 

Dioxide, 

CO, 

Per Cent. 

• 17 

.47 

3.96 

1.09 

1.37 

Sulphur 
Trioxide, 
SO , 

Per Cent. 

46.30 

46.12 

46.20 

42.01 

53.56 

56.54 

Magnesia, 

MgO 

Per Cent. 

.12 

.34 

.60 

trace 

Lime, 

CaO 

Per Cent. 

32.49 

32.90 

32.35 

83.96 

38.04 

42.04 

1 S<5 . 

^ 6 ^ § 

<L> < ^ I_ 

'O . O <D 

O 

.12 

trace 

.10 

.67 

.16 

trace 

Silica, 

SiOi 

Per Cent. 

.35 

.11 

.10 

11.97 

.85 

trace 


in 

i < 

cS 

• H 

Ih 

<X> 

-M 

nj 

krH 

<3 


o m 

oJ £ 

S § 
8 2M 

3 °1 m co 
S > £ -g 

d O D » 


in 
aS 
to 

a 

Cj 

M 

to" 4J 

•c s 


ctf 

Ph 


ass, 

3 s 3 s 

co to CO 4-> 

a. a, w 

COOP 


o o 


a) 

6 

<V 
<J 

w 


0) CL) 

-4-> c! 

% & 

co a) 

S W 


ing the No. 100 sieve. 
A four-roller Raymond 
mill will grind 4 to 5 
tons of gypsum per 
hour to this fineness. 
When burrstones are 
employed a 42-incb 
stone is usually em¬ 
ployed for the raw 
gypsum and a 36-inch 
stone for grinding the 
rej ects f rom the screens, 
which are usually of 
the shaking type. A 
combination of 42-inch 
and 36-inch burrstones 
will grind about 2 tons 
per hour to a fineness 
of 80 per cent, passing 
the No. 100 sieve. 

The coal required to 
calcine gypsum is usu¬ 
ally between 80 and 
00 pounds per ton of 
plaster produced. Less 
coal is required when 
the gypsum is dried 
before being ground. 

30. Gypsum is also 
calcined in rotary 
driers. These consist 
of cylinders of sheet 
steel mounted on roll¬ 
ers. The gypsum is 
heated in these cylin¬ 
ders to about 400° F. 
and while at this tem- 


386—3 






























30 


MANUFACTURE OF CEMENT, PART 1 


perature it is elevated into bins where the residual heat in 
the material completes the calcination. The driers used are 
similar to those employed for drying coal and rock in the 
manufacture of Portland cement and are described in detail 
later. The rotary process differs from the kettle process 
of calcination in this respect that the gypsum is merely crushed 
to a size that will pass a 1-inch ring screen before being calcined, 
after which it is ground to the required fineness. 

31 . Cement Plaster.—If the gypsum used for making 
plaster of Paris is pure the calcined product will set very 


TABLE Y 

STRENGTH OF FINISHING PLASTERS 


Kind of Plaster 

Age of Briquettes 

1 Day 

7 Days 

28 Days 

Tensile Strength in Pounds per 
Square Inch 

Plaster of Paris, neat. 

228 

393 

445 

1 part plaster of Paris and 




1 part sand . 

87 

320 

368 

1 part plaster of Paris and 




2 parts sand . 

55 

203 

212 

1 part plaster of Paris and 




3 parts sand. 

35 

148 

145 

Keene’s cement. 

367 

669 



rapidly when mixed with water. If, however, the gypsum 
contains a large percentage of impurities the resulting plaster 
will set more slowly. The same result can also be obtained by 
adding certain retarders to plaster of Paris made from pure 
gypsum. Since a slow-setting plaster can be handled more 
conveniently than a quick-setting one, it is customary to add 
2 to 10 pounds of some retarder to every ton of plaster and the 
resulting product is generally marketed as cement plaster 






















MANUFACTURE OF CEMENT, PART 1 


31 


stucco. The materials used as retarders are usually of an 
organic nature, as glue, sawdust, blood, packing-house tank¬ 
age, etc., and are non-crystalline in character. Colloidal, or 
non-crystalline, substances, such as clay, etc., can also be used 
as retarders. Hence, gypsum containing clay makes a slow- 
setting plaster. 

32 . Wall Plaster.— Cement plaster to which has been 
added a certain percentage of fine picked hair in about the 
proportion of 2 or 3 pounds of hair to a ton of plaster, is 
known as wall plaster. In place of hair wood fiber is now used 
a great deal, about 75 to 150 pounds of the fiber being added 
to a ton of plaster. 

33 . Hard-Finish. Plaster. —In manufacturing hard- 
finish plasters, gypsum is completely dehydrated by heating 
to a high temperature. The calcined material is then immersed 
in a solution of alum and after drying it is again calcined at 
a red heat. The resulting product is ground very finely, when 
it is ready for the market. Chief among the hard-finish plas¬ 
ters is Keene’s cement, which was originally manufactured in 
England but on which the patents have expired. 

34. Composition and Tests of Plasters. —Table IV 

gives the composition of several samples of gypsum, plaster, 
etc., and Table V gives the strength of several finishing 
plasters. 


32 


MANUFACTURE OF CEMENT, PART 1 


CEMENTS 


NATURAL, ROMAN, AND ROSENDALE CEMENTS 


COMPOSITION AND PROCESSES OF MANUFACTURE 

35. Classification. —Strictly speaking, natural, Roman 
and Rosendale cements all belong to one class, their com¬ 
positions and the process of their manufacture being similar. 
They are frequently erroneously called hydraulic. This is a 
misnomer, since slag and Portland cements are also hydraulic, 
but they are very different from natural or Rosendale cement, 
both in composition and properties. Natural cement is some¬ 
what similar to hydraulic lime. Instead of slaking with water, 
however, after burning it is pulverized, exposed to the air to 
season and then put on the market in powdered form. Instead 
of having a loss on ignition of 8 to 21 per cent, as in hydraulic 
limes, this loss is less than 5 per cent, and the resulting cement 
is much stronger. In a strict sense the name Rosendale is a 
local one, being applied originally only to cements from the 
cement district of Ulster County, New York. Other manu¬ 
facturers in various sections of the country coming into the 
market later with similar products used the name Rosendale, 
whereas Natural or Roman would have been better. 

36. Composition and Properties of Natural 
Cements. —Natural cements made from American rocks 
will show a specific gravity of 2.8 to 3.15, a little lower than 
the specific gravity of Portland cement. The natural cements 
set much more rapidly than Portland cements, but their setting 
time may be retarded to some extent by the addition of plaster 
of Paris, or by aeration. They should require at least 10 min¬ 
utes to gain their initial set and should be hard-set in 3 hours. 
They harden much more slowly than Portland cement, but 




£ 

3 

PQ 


► 


<1 

K 

P 

H 

< 


XJl 

P 

O 

H 

« 

4 

P 

P 

o 

£ 

o 

M 

H 

H 

GO 

O 

P 

a 

o 

p 


r 

O -M 

«r&5 S 

8 + o 
^cS & 

P) IP 

2.00 

7.04 

5.42 

4.50 

6.90 

3.07 

9.50 

o . 

«r <5 -g 

rt + o 
-O fc 

7.42 

1.80 

1.62 

2.51 

Magnesia, 

MgO 

Per Cent. 

15.00 

17.26 

9.50 

11.63 

14.82 

22.24 

.21 

22.60 

Lime, 

CaO 

Per Cent. 

48.18 

33.04 

44.65 

36.50 

34.64 

41.60 

52.12 

33.40 

Iron Ox¬ 
ide, Fe 2 03 
Per Cent. 

3.35 

.80 

1.43 

4.78 

4.68 

2.80 

2.60 

2.80 

Alumina, 

A.I 2 O 3 

Per Cent. 

7.23 
"* 10.60 
7.85 
11.23 
10.96 
4.40 
10.36 
4.00 

Silica, 

Si0 2 

Per Cent. 

22.56 

27.60 

25.28 

29.92 

28.91 

20.20 

30.40 

25.00 

Where Made 

Georgia 
Illinois 
Kentucky 
Maryland 
New York 
New York 
Pennsylvania 
Wisconsin 

Brand 

Howard. 

Utica. 

Hulme Star. 

Cumberland. 

Hoffmann. 

Akron Star. 

Bonneville Improved 
Milwaukee. 


33 



































34 


MANUFACTURE OF CEMENT, PART 1 


develop very good strength in time. They are not usually so 
finely ground nor can they be used for the better grades of 
concrete work. 

Table VI gives the composition of some of the best known 
American cements. 

37. Natural-Cement Rock.— The rock from which 
natural or Roman cement is manufactured consists of an 
impure limestone containing from 20 to 30 per cent, of clay. 
It is necessary that this limestone should be of uniform com¬ 
position and very fine grained. The mixture of calcium car¬ 
bonate and clay must be very intimate and no rock made up 
of bands of pure limestone and shale or slate is suitable for 
the manufacture of natural cement no matter what its average 
analysis may be. Magnesium carbonate up to 30 per cent, may 
be present in the rock; natural cements made from low mag¬ 
nesian rock, however, are just as good as those made from 
magnesian limestone. 

38. Process of Manufacturing Natural Cement. 

The process of manufacturing natural cement differs mate¬ 
rially from that of making Portland cement. Except possibly 
for crushing by sledges and sorting into coarse and fine, the 
raw material undergoes no preliminary preparation before 
burning, but is taken from the quarry or mine directly to the 
kilns. After burning and grinding the cement is ready for 
use. For burning the raw material the kilns are of the vertical 
type and are simple in construction and similar to the mixed- 
feed lime kilns. The operation of burning is the same as for 
lime, anthracite coal being employed as a fuel. 

As the rock is calcined at a low temperature the amount of 
fuel used is small, varying with improved kilns from 6 to 
15 per cent, of the weight of cement produced. The material 
drawn from the bottom of the kiln is sometimes sorted, the 
hard or overburned pieces being discarded and the remainder 
put through grinding mills. More often, however, the entire 
product is ground and sent to the stock house or the packing 
house. A kiln of the dimensions indicated in Fig. 1 produces 
from 90 to 100 barrels of cement per day. 



'////w/ZtyA. 

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MANUFACTURE OF CEMENT, PART 1 35 

39. Pulverizing Natural-Cement Rock.— The ma¬ 
chinery for pulverizing natural-cement rock after burning 
differs from that described later in connection with the Port¬ 
land cement-making process, the ball mills or Griffin mills, 
which are indispensable in Portland cement plants, being used 
only in plants producing both Portland and natural cement. 
There are two reasons for this: first, the lightly burned rock 


corresponding to clinker in the Portland process, is much more 
readily ground than clinker; second, the requirements as to 
fineness are not so rigid as for Portland cement. A com¬ 
mon practice in grinding is to put the burned rock through 
vertical crackers similar to coffee mills which reduce about 
25 per cent, of the material to a merchantable fineness. This 
is separated by screens and sent to packers. The remainder 


Fig. 9 




































































































































































36 


MANUFACTURE OF CEMENT, PART 1 


is pulverized to the required fineness by the old-fashioned burr- 
stone mill, or by rock-emery mills. 

The burrstone mill, as shown in Fig. 9, consists of two 
stones a and b with dressed faces, the lower one b revolving 
and grinding the cement between it and the stone a. Each 
millstone usually consists of one piece of burrstone or quartzite. 
From time to time the stones are redressed and furrows 
running radially are cut in the stones to facilitate grinding. 

The rock-emery mill is similar to the burrstone, but, as the 
name indicates, rock emery is used for the grinding surfaces. 


POZZULAN CEMENTS 

40 . Pozzulanic Materials.— The materials used in the 
manufacture of pozzulan cement may be of either natural 
or artificial origin, consisting of those substances which are 

TABLE VII 


COMPOSITION OF POZZULANIC MATERIALS 


Material 

Silica, 

SiOi 

Per Cent. 

Alumina, 

AI 2 O 3 

Per Cent. 

Iron 
Oxide, 
FezOi 
Per Cent. 

Lime, 

CaO 

Per Cent. 

Mag¬ 

nesia, 

MgO 

Per Cent. 

Soda, 

NaiO 

Per Cent. 

Potash, 

KzO 

Per Cent. 

Pozzulan .... 

42.00 

15.50 

12.50 

9.47 

4.40 



Trass. 

48.93 

18.95 

12.34 

5.40 

2.31 



Santorin 








earth. 

66.37 

13.72 

4.31 

2.98 

1.29 

4.22 

2.83 

Blast-furnace 








slag. 

32.28 

12.50 

5.14 

48.00 

2.00 




capable of forming hydraulic cements simply by being mixed 
with lime. No heating or further treatment is necessary. The 
natural pozzulanic materials are widely distributed and usuallv 
consist of fine volcanic ash or dust (pozzulan, trass, santorin) 
deposited either on the slopes of a volcano or carried by the 
winds to lakes or streams and deposited there. The word 
pozzulan comes from the little town of Pozzuoli at the foot 
of Mount Vesuvius where the volcanic ash was obtained by 






























MANUFACTURE OF CEMENT, PART 1 


37 


the Romans for their cement. This volcanic ash resembles 
blast-furnace slag in composition, as indicated in Table VII. 

Natural puzzolanic materials of domestic origin have never 
come into use and only a very little cement made from such 
natural materials has been imported into the United States. 
Of all the puzzolanic materials blast-furnace slag is by far the 
most important. 

41 . Process of Manufacturing Pozzulan Cement. 

What is known as slag cement is made by granulating slag as 
it runs from the furnace by means of a jet of water; it is 
then dried in revolving dryers, mixed with the proper propor- 


T ABLE VIII 

COMPOSITION OF SLAG CEMENTS 


Source of Samples 

Silica, 

SiOt 

Per Cent. 

Iron Ox¬ 
ide and 
Alumina, 
F e-iOz + 
AI 2 O 3 

Per Cent. 

Lime, 

CaO 

Per Cent. 

Magnesia, 

MgO 

Per Cent. 

Sulphur, 

5 

Per Cent. 

Loss on 
Ignition 
Per Cent. 

Chicago, Illinois. . . . 

27.20 

14.18 

50.03 

3.22 

1.40 

4.25 

Chicago, Illinois.... 

29.80 

12.30 

51.14 

2.34 

1.37 

2.60 

Chicago, Illinois.... 

27.80 

11.10 

50.96 

2.23 

1.18 

5.30 

North Birmingham, 







Alabama. 

27.00 

12.00 

55.00 




Ensley, Alabama.... 

27.78 

11.70 

51.71 

1.39 

1.31 



tion of slaked lime, and ground so fine that from 90 to 95 per 
cent, of the product will pass through a 200-mesh sieve. This 
powder is the finished product. 

Not all slags are adapted to the making of cement. The 
composition of such slags must lie within the following limits: 
Silica, not over 49 per cent.; alumina, from 12 to 17 per cent.; 
magnesia, under 4 per cent. 

42 . Properties and Composition of Slag Cements. 
Slag cements set very slowly and accelerators are usually 
added to quicken the set. In the Whiting process caustic soda 
and potash or sodium chloride are added for accelerating pur¬ 
poses. Slag cements are usually much lighter in color than 





















38 


MANUFACTURE OF CEMENT, PART 1 


Portland cement, varying from bluish-white to yellow, and 
they also have a much lower specific gravity—from 2.7 to 2.8. 
Slag cements show good tensile strength when tested with sand, 
but have slight resistance to abrasion, or, in other words, 
wear poorly and are therefore unsuited for making floors, 
sidewalks, etc. The slag cements are also considered much 
better for use under water than in dry air. 

Table VIII gives the composition of some slag cements. 


PORTLAND CEMENT 


CHARACTER AND COMPOSITION 

43. What is commonly known as Portland cement may be 
defined as the finely pulverized product resulting from the 
calcination to incipient fusion of an intimate mixture of prop¬ 
erly proportioned argillaceous and calcareous materials and to 
which no addition of other material greater than 3 per cent, is 
made subsequent to calcination. The general steps in the 
process of manufacture are shown in Fig. 10. 

44. Composition of Portland Cement.—The average 
composition of a number of American Portland cements is 
given in Table IX. 

The essential elements of Portland cement are silica, alumina, 
and lime. A small amount of the alumina is always replaced 
by iron, however, and some of the lime by magnesia owing to 
the presence of these elements as impurities in the raw mate¬ 
rials. Calcium sulphate in the form of gypsum or plaster of 
Paris is always added to regulate the set. Carbon dioxide and 
water, usually reported together in an analysis and called loss 
on ignition, are gradually absorbed by the cement during 
grinding and in storage. 

45. Influence of Lime. —Portland cement usually con¬ 
tains from GO to G4 per cent, of lime. Up to a certain limit 
it may be said that the more lime there is present in the cement 
the greater will be its strength. The limit is reached, how^ 




MANUFACTURE OF CEMENT, PART 1 


39 


ever, when more lime is present than will combine chemically 
with the silica and alumina, thus leaving some lime in the 
uncombined state. Lime in slaking expands so that an excess 
of lime over what will unite with the silica and alumina will 
cause the cement to expand, or blow, as it is technically termed, 
and crack. High-lime cements are usually very slow-setting 
but they harden rapidly, sometimes reaching their maximum 



Fig. 10 


strength in 28 days. Low-lime cements are likely to be quick¬ 
setting. Hence, one of the remedies for quick-setting cement 
is to increase the quantity of lime in the raw mixture. 

The amount of lime that a cement may contain depends 
on the care with which the mixture of raw materials is made. 
Thus, poorly ground, imperfectly mixed raw materials would 
probably result in a very much overlimed cement if the lime 




















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41 


MANUFACTURE OF CEMENT, PART 1 


limit as shown by chemical analysis of the clay, marl, lime¬ 
stone, or cement rock of the mixture were almost reached. 
The coarse particles of calcium carbonate would not come 
into contact with the silica and alumina sufficiently close to 
combine with them completely. A properly burned cement 
will also stand a greater percentage of lime than one which is 
improperly burned. A cement in which the temperature at 
burning was too low to heat all the lime to the point of com¬ 
bination with the silica and alumina, would naturally contain 
free lime. The percentage of lime to be carried at any Port¬ 
land cement works is usually controlled by two things—the 
setting time and the soundness. Enough lime must be presept 
to keep the cement from being quick-setting either when made 
or after seasoning and not so much lime that the cement will 
fail when tested for soundness. With raw materials high in 
alumina, the margin between maximum and minimum limits 
is small. With such materials extreme care is needed in the 
process of manufacture and the raw materials should be very 
finely ground and the burning should be thorough. When the 
amount of alumina is low the margin is much greater, but if 
the amount of lime is nearly up to the maximum a stronger 
cement will result. 

4G. Influence of Silica. —Silica next to lime is the most 
important constituent of Portland cement. It is present in 
the proportion of 19 to 25 per cent., cements containing the 
latter percentage of silica being low in alumina. High-silica 
cements are usually slow-setting and of good tensile strength. 
Increasing the amount of silica usually increases both strength 
and length of setting time. It also increases the temperature of 
burning. Cement, in order to prevent it from being quick¬ 
setting, should contain at least two and one-half times as much 
silica as alumina. 

47. Influence of Alumina. —Portland cement usually 
contains between 5 and 10 per cent, of alumina. As the per¬ 
centage of alumina rises the cement sets more quickly, and 
when the amount of alumina reaches 10 per cent, or more, the 
cement becomes very quick-setting with a corresponding 


42 


MANUFACTURE OF CEMENT, PART 1 


decrease of tensile strength. Clinkers obtained on burning 
mixtures high in alumina are very fusible, hard to burn 
uniformly, and difficult to grind. 

48. Influence of Iron Oxide. —Iron oxide in the 
cement mixture acts as a flux and promotes the combination 
of silica and lime. Mixtures of silica, alumina, and lime in 
the proportions usually found in cement are extremely hard 
to burn. Iron, however, greatly lowers the temperature of 
burning. One of the cures for unsound cement is therefore 
found in the replacement of clays high in alumina by those 
high in iron. As it does not seem to make cement quick¬ 
setting, iron may be made to replace alumina to advantage in 
many instances. Portland cements containing high percentages 
of ferric oxide show great resistance to the disintegrating 
influence of the salts of magnesium, etc., found in sea-water. 

Cements high in iron oxide are difficult to grind, as much 
iron produces a very hard clinker. The color of cement is 
due to the presence of iron oxide. White Portland cement is 
made from materials low in iron, such as very pure limestone 
and white clay, and burned with oil. As a result of this, the 
resulting cement contains less than .5 per cent, of iron oxide. 
The clinker is a light green and, when ground, gives a white 
cement. 

49. Influence of Magnesia.— A cement containing 
1^ per cent, of magnesia was long considered dangerous; at 
present, however, 5 per cent, is thought to be harmless and 
the standard specifications allow this amount in cement. The 
popular supposition is that in time any considerable amount 
of magnesia causes cement to expand and crack. 

50. Influence of Sulphates.— The effect of calcium 
sulphate is to delay the setting of cement. For this reason 
calcium sulphate in the form of gypsum or plaster of Paris 
is always added to cement after burning. The standard 
specifications permit manufacturers to add as much as 3 per 
cent, of calcium sulphate in order to give the cement slow- 
setting properties. Although the presence of calcium sul¬ 
phate in small quantities is beneficial to cement, there is no 


MANUFACTURE OF CEMENT, PART 1 


43 


doubt that more than 4 or 5 per cent, is injurious. The 
standard specifications allow 2 per cent, of sulphur trioxide, 
S0 3 , in Portland cement. 


RAW MATERIALS FOR PORTLAND CEMENT 

51. Variety and Source of Raw Materials.— Port¬ 
land cement is manufactured from a variety of raw materials. 
Those used may be classed as calcareous or argillaceous, 
according as the lime or the silica and alumina predominate. 
The calcareous materials consist of limestone, marl, chalk, and 
alkali waste; the argillaceous materials consist of clay, shale, 
slate, and cement rock. 

Any combination of materials from these two groups that 
will give a mixture of the proper composition for burning may 
be used, but as a rule the combinations used in the United 
States are as follows: 

1. Cement rock and limestone, which is used in the famous 
Lehigh Valley cement district of Pennsylvania and New Jersey. 

2. Marl and clay or shale, which is used principally in 
Michigan, Ohio, Indiana, and Central New York. 

3. Limestone and shale or clay, which is used in many parts 
of the country, as these materials are widely distributed. 

4. Blast-furnace slag and limestone, which is used in plants 
located in Illinois, Ohio, Minnesota, and Pennsylvania. 

5. Caustic-soda waste and clay, which is used by one large 
plant in Michigan. 

52. Cement Rock. —Limestone, to be suitable for cement 
manufacture, should contain but little carbonate of magnesia, 
6i per cent, being about the limit. It should also be free from 
quartz either in the form of sand or flint pebbles. Occasionally 
narrow veins of flint running through the limestone bed will 
not be harmful because the flint may be sorted out in quarrying. 
Since the limestone must be reduced to a fine powder in order 
to mix intimately with the clay or shale used with it, its 
hardness is an important point in determining its suitability 
for cement manufacture because fine grinding of the raw 
materials is essential in order to make a sound cement. The 



44 


MANUFACTURE OF CEMENT, PART 1 


value of limestone for cement making will be influenced to 
some extent by the composition of the other material used 
with it. 

The impure clayey limestone used for the manufacture of 
Portland cement in the Lehigh District is known technically 
as cement rock . This rock forms a narrow belt extending 
in a northeasterly direction from Reading, Pennsylvania, to 
a few miles north of Stewartsville, New Jersey. It passes 
through Berks, Lehigh, and Northampton counties in Penn¬ 
sylvania, and Warren County in New Jersey, and is about 
50 miles long and not over 4 miles at its greatest width. It 
has been found by experience that a mixture containing about 
75 per cent, of calcium carbonate and from 18 to 20 per cent, 
of clayey matter gives the best Portland cement, and the 
impure limestones found in the Lehigh Valley approach this 
composition. When this cement rock contains less than 75 per 
cent, of calcium carbonate, it is necessary to add a sufficient 
amount of pure limestone to make up the deficiency. When the 
rock contains more than 75 per cent, of calcium carbonate, it 
is necessary to add a little slate or clay. Cement rock is much 
softer than the pure limestones and consequently is much more 
easily ground. The nearer it approaches the required com¬ 
position for cement mixture, the more valuable it is. Rock 
requiring a small admixture of clay will prove more economical 
than one requiring the addition of limestone since the cement 
rock is usually overlaid by clay that has to be removed in 
order to get at the rock. 

At several mills in the Lehigh district neither clay nor lime¬ 
stone is needed and the composition of the cement is controlled 
by mixing rock high in lime from one part of the quarry with 
rock low in lime from another part. 

53s. Marl.— Marl is more or less pure calcium carbonate, 
the principal impurities being clay, organic matter, and car¬ 
bonate of magnesia. Marl beds usually occupy the beds of 
lakes, either present or extinct, and are formed by the pre¬ 
cipitation of calcium carbonate from the water by the agency 
of certain algae, or water plants. Marl is soft and powdery, 


MANUFACTURE OF CEMENT, PART 1 


45 


the larger part of it passing a 200-mesh cement-testing sieve. 
It therefore requires little grinding before burning. White 
marls are usually free from organic matter, but the gray 
marls often contain from 5 to 10 per cent, of impurities. 
Marl beds vary in size from a few acres up to two or three 
hundred. A cubic foot of marl generally contains about 
47.5 pounds of marl and 48 pounds of water. Marls for use 
in Portland cement manufacture should be free from sand 
and pebbles. Some marls contain a considerable percentage 
of sulphur. Just how much sulphur is allowable is hard to 
say, but at least 5 or 6 per cent, of S0 3 might be present with¬ 
out rendering the marl unfit for the manufacture of Portland 
cement. The value of a marl bed will usually lie in its depth, 
area, and physical characteristics rather than in its chemical 
composition. The greater the depth of the bed, the more 
economically it can be worked. If the beds are dry so that 
the dry process of manufacture can be employed, the value of 
the deposit is greatly increased thereby. Chemically the marl 
should contain at least 75 per cent, of calcium carbonate and 
not over 6J per cent, of magnesia. It should also be practically 
free from coarse quartz sand. 

54. Clay. —Clay consists of a mixture of kaolin with 
more or less sand and other impurities. Kaolin, or kao- 
linite, is a hydrated silicate of alumina having the formula 
Al 2 0 z -2SiO 2 -2H 2 0 . Sand is composed of grains of quartz and 
other minerals. Clay used for Portland cement manufacture 
should contain at least two and three-tenths times as much silica 
as alumina. Iron may replace alumina in almost any quantity 
without injuring the cement. Magnesia and lime are usually 
present only in small quantities, the more of the latter present 
the better, but the amount of magnesia should not be over 3 or 
4 per cent. The amount of alkalies present should not run 
over 3 per cent., as an excess is likely to cause unsound and 
quick-setting cement. All clay contains some uncombined 
silica in the shape of quartz sand or pebbles. Ihe sand must 
be present in the clay in a very finely divided condition. If 
much more than 5 per cent, is present in the form of grains 


386—4 


46 


MANUFACTURE OF CEMENT, PART 1 


that will not pass a 100-mesh sieve, the clay is not suited for 
cement purposes. 

55. Shale. —For cement-making purposes shale may be 
looked on as solidified clay, the chemical composition of clay and 
shale being very similar. For mixing with limestone shale is 
preferable to clay because segregation of the two is less likely 
to take place. Shale also carries less water and consequently 
does not require so much drying before grinding. Clays are 
better suited to mixing with marls because of the similarity 
of their physical properties. 

5G. Slag:. —Slag suited to the manufacture of Portland 
cement can come only from iron furnaces working on pure 
ores such as those of the Lake Superior mines and fluxed with 
low magnesian limestone. Generally speaking, the slag must 
have a composition within the following limits: Silica and 
alumina, not over 48 per cent.; iron and alumina, 12 to 14 per 
cent.; magnesia, under 3 per cent. 

57. Composition of Materials. —Table X shows the 
composition of various materials used for the manufacture 
of Portland cement. 

58. Valuation of Raw Materials for Portland 
Cement. —In passing on the availability of raw material, a 
number of things besides the results of analysis must be con¬ 
sidered. The cost of quarrying or excavating, the power 
required to grind the material, and the coal required to burn 
it must be taken into account. Marl and clay are the raw 
materials easiest to excavate, but. on the other hand the cement¬ 
making plant can seldom be located near the beds of the former, 
owing to the necessity of having the mill on firm dry ground. 
In some instances this requirement necessitates pumping or 
carrying the marl several miles, which increases the cost of 
manufacture. A very shallow marl bed cannot be worked 
so economically as a deep one because of the constant mov¬ 
ing about of the excavating apparatus, etc. When the marl 
beds are located in the North cold weather is likely to tie the 
beds up by the freezing of the lake over them, necessitating 


TABLE X—COMPOSITION OF RAW MATERIALS USED IN THE MANUFACTURE OF PORTLAND CEMENT 


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48 


MANUFACTURE OF CEMENT, PART 1 


either the cutting of the ice or the shutting down of the mill, 
either one or both of which contingencies add to the cost of 
production. Cement rock is usually blasted down, loaded on 
cars, and hauled by cable to the mill, which is usually close 
at hand. Cement rock costs more than marl in explosives and 
drilling, but if a steam shovel is used to load the cars it costs 
less to convey to the mill after it is down, as only half as much 
material has to be handled owing to the water in the marl. 
Limestone is harder than cement rock and costs more to drill 
and blast; it also costs more to break up the lumps into sizes 
suitable for loading on the cars or carts. The cost of quarry¬ 
ing and loading shale will be about the same as in the case of 
cement rock. The cost of getting out either cement rock or 
limestone will be influenced by the amount of stripping, or 
removal of soil above the deposit, that has to be done. In some 
mills this top material can be used, in which case the cost of 
removal is saved. 

59. Mar l and clay are the easiest materials to grind; shale , 
cement roc k, and chalky limestone come next, while limestone 
and slag are harder still. Cement-rock limestone mixtures 

—* V 

burn the easiest of any of the combinations in the kilns, lime¬ 
stone-clay and slag-limestone mixtures are harder still, and the 
wet marl and clay mixtures require much more coal than any 
of the others. 

The mere fact that raw materials of suitable chemical com¬ 
position for the manufacture of Portland cement exist in a 
certain locality is no reason why a mill should be erected on 
the site, because the success of the enterprise will depend more 
on local conditions than on raw materials themselves. The 
cost of fuel, labor, and supplies, as well as ability to market 
the product, must be taken into consideration. The fuel item 
in the manufacture of Portland cement is a big one, dry 
material requiring from 165 to 200 pounds of fuel per barrel 
of cement, and wet material from 200 to 250 pounds under the 
usual system for burning and grinding. Portland cement is 
so bulky in proportion to its value that the nearness of the mill 
to the market is also an important item. 




MANUFACTURE OF CEMENT, PART 1 


49 


CALCULATING PORTLAND-CEMENT MIXTURES 

GO. In spite of considerable research, the composition of 
Portland-cement clinker is by no means thoroughly understood. 
The best opinions, however, seem to agree that there are cer¬ 
tainly two essential compounds in ideal clinker. These com¬ 
pounds are tricalcium silicate, 3 CaO-Si0 2 , and tricalcium 
aluminate, 3 Ca0-Al 2 0 3 . A less desirable compound always 
present in cement is the dicalcium silicate, 2Ca0Si0 2 . The 
tricalcium silicate is, of course, more basic and contains 50 per 
cent, more lime than the dicalcium silicate. Unquestionably, 
the nearer cement comes to being composed of only tricalcium 
silicate and tricalcium aluminate, the better it is. This is 
another way of saying that so long as it is in combination with 
the silica and alumina, the more lime that cement contains the 
better it is. The tricalcium aluminate has the following com¬ 
position :* 

Alumina, Al 2 0 3 = (27X2) + (16X3) =54+48 = 102 
Lime. 3CaO = (40+16)3 = 168 

Hence, there is present xff=1.65 times as much lime as 
alumina. Similarly the tricalcium silicate contains 2.8 times 
as much lime as silica. Now, in order to form tricalcium 
aluminate there must be present 1.65 pounds of lime for every 
pound of alumina in the cement mixture; similarly, for every 
pound of silica there must be 2.8 pounds of lime. Thus, 
2.8 pounds of lime is equivalent to 5 pounds of calcium 
carbonate (CaC0 3 : CaO = 5 : 2.8, or 100:56 = 5:2.8) and 
1.65 pounds of lime is equivalent to 2.95 pounds of calcium 
carbonate (100:56 = 2.95:1.65). 

To express these relations in the shape of formulas, let 
X = percentage of calcium carbonate in any cement mixture; 
a = percentage of silica; 
b — percentage of alumina; 
y — percentage of lime. 

Then, x = 5a+2.95 6 (1) 

y = 2.8 a + 1.65 b (2) 

*For convenience in calculation, the atomic weights are taken as 
follows: Ca= 40, 0=16, Al= 27, C=12, and Si-28. 




50 


MANUFACTURE OF CEMENT, PART 1 


These formulas give the maximum amount of lime that a 
cement could carry if it were manufactured under ideal con¬ 
ditions of grinding and burning. Under the conditions met 
in actual practice, however, it is not possible to grind the raw 
material fine enough to allow all the lime to combine with the 
silica and alumina; and, since an excess of clay is less harmful 
than an excess of lime, it is customary to allow a slight margin 
between the lime actually present in the mixture and the 
theoretical lime requirements. It has been found in practice 
that from 90 to 92 per cent, of the lime required by the 
formula is all that can be safely used. Taking 90 per cent, 
as the maximum, formula 1 becomes 

x = 4.5 a + 2.7 b (3) 

61. In order to show the method of using the formula, 
let it be required to make a cement mixture from limestone 
and cement rock of the following compositions: 



Cement Rock 

Limestone 

Silica. 

. . . . 19.06 

2.14 

Iron oxide. 

. . . . 1.14 

.46 

Alumina. 

. . . . 4.44 

1.00 

Calcium carbonate . . . 

.... 69.24 

94.35 

Magnesia. 

. . . . 4.21 

2.18 


The calculation of the mixture is as follows: 

Limestone 

Total calcium carbonate. 94.35 

CaCOz needed for the silica present 2.14X4.5 = 9.63 
CaCOz needed for the alumina present 1.00X2.7 = 2.70 12.33 

Available calcium carbonate. 82.02 

Cement Rock 

CaCOz needed for the silica . . . .19.06X4.5 = 85.77 
CaCOi needed for the alumina . . . 4.44X2.7 = 11.99 97.76 

Less calcium carbonate contained. 69.24 

Required calcium carbonate for 100 parts . . 28.52 

The number of pounds of limestone required for 100 pounds 
of cement rock will then be 


28.52X100 


35, nearly 


82.02 














MANUFACTURE OF CEMENT, PART 1 51 

Now 35 pounds of limestone contains 

.35X94.35= 33.02 pounds CaCOz 

100 pounds of cement rock con- 

_ tains. 69.24X100= 69.24 pounds CaCOz 

135 pounds of mixture contains 102.26 pounds CaCO% 

The mixture would therefore analyze 

102.26X100 ^ , r 

-= 75.7 per cent, of calcium carbonate 

135 

62. The whole operation of calculating cement mixtures 
may be condensed into one formula, as follows: 

x= (AX4.5+RX2.7)-C 
c-(aX4.5+6X2.7) 

in which X = percentage of limestone or marl needed per ton 

or per pound of cement rock or clay; 

A = percentage of Si0 2 in cement rock or clay; 

B = percentage of A/ 2 0 3 in cement rock or clay; 

C = percentage of CaCOs in cement rock or clay; 
a = percentage of Si 0 2 in limestone or marl; 
b = percentage of Al 2 0 3 in limestone or marl; 
c = percentage of CaCOz in limestone or marl. 

Cement mixtures proportioned by this formula will be 
neither overlimed nor underlimed, and the resulting cement, 
if the mixture has been properly ground and burned, will give 
good results when tested for strength and soundness. 

The preceding formula is very useful for calculating cement 
mixtures from complete analyses, as in making laboratory trial 
burnings, starting up a new mill, or opening a new deposit. 
However, it will be found more practicable in actual mill 
routine work to fix on a certain percentage of calcium carbonate 
found by experience to give satisfactory results and to keep 
the mixture as near this percentage as possible. Provided 
the amount of water, organic matter, and magnesia in the 
raw materials is constant, it will be comparatively easy to keep 
a fairly uniform mixture by merely watching the percentage 
of calcium carbonate. 







52 


MANUFACTURE OF CEMENT, PART 1 


63. The mathematical part of calculating cement mixtures 
for a fixed lime standard may be simplified by the following 
formulas, the first of which is for use when the cement rock 
is weighed and the proper proportion of this weight of lime¬ 
stone is added: 

To find the percentage of a given limestone to be added 
to a given cement rock or clay to make a given mixture, let 

X = percentage of limestone necessary; 

L = percentage of CaCOz in limestone; 

R = percentage of CaCOz in rock or clay; 

M = percentage of CaCOz desired in the mixture. 


Then, 


LX + 100 R 

100+A 


= M 


or 


L X+ 100 R = 100 M+XM 
LX-MX= 100 M —100R 
X{L-M) = (M-R) 100 



M —R 
L-M 


X 100 



Also, 


X _ M — R _ limestone 
100 L — M cement rock 


Hence, 

limestone: cement rock = (M — R):(L — M) 


Example.— What percentage of limestone analyzing 95 per cent. 
CaC0 3 must be added to a cement rock analyzing 70 per cent. CaCOa 
to give a mixture analyzing 75 per cent. CaCoR 


Solution.— The percentage of limestone 
formula 1 ; thus, 


75 - 70 
95 - 75 


X 100 


500 

20 


is found by applying 
= 25 


Hence, to every 100 lb. of cement rock 25 lb. of limestone must be 
added. Ans. 


The second formula is practically the same as the preceding 
one, but it is intended for use when the limestone or marl is 
weighed and the proper proportion of this weight of clay or 
shale is added. 









MANUFACTURE OF CEMENT, PART 1 


53 


To find the percentage of a given clay or shale (or cement 
rock) to be added to a given marl or limestone to make a given 
mixture, let 


X = percentage of clay or shale necessary; 

C = percentage of CaO in clay or shale; 

L = percentage of CaO in marl or limestone; 
M = percentage of CaO desired in the mixture. 

L — M 

X = -—— X 100 (2) 

M —C 

X _ L — M _ limestone 
100 M — C clay 
limestone : clay = ( L — M) : (M — C) 


Then, 

Also, 

Hence, 


Example. —What percentage of clay analyzing 2.5 per cent. CaO 
must be added to a limestone containing 53 per cent. CaO to obtain a 
mixture analyzing 41.0 per cent. CaO ? 

Solution. —The percentage of clay is found by applying formula 2; 


thus, 


X = 


53-41 


f X 100 = 


1,200 


= 31. Ans. 


41-2.5 38.5 

Instead of percentages of CaO, percentages of CaCO z may 
be used, but, if used in one case, must be used in all. 


QUARRYING OF DRY MATERIALS 

64. Limestone, cement rock, and shale are usually quarried, 
while clay is dug from pits and marl is often dredged from 
lakes and similar bodies of water. Deposits of cement rock' 
and limestone are usually overlaid by a few feet of soil and 
clay, which must be removed by scrapers or by shoveling. 
When clay is used to make the mixture, this surface deposit 
is conveyed to the mill; otherwise it is carted away to a dump. 
Some deposits of rock and limestone are so situated that they 
can be opened on a hillside; with others it is sometimes neces¬ 
sary to dig straight down into the earth. 

The stone is usually blasted down in benches, sometimes 
along the whole face of the quarry at once; at other quarries, 
only a small part of a bench at a time. The drill holes for 
the blasting are made with power drills operated by steam 
or compressed air, and these holes are carried to a depth of 









54 


MANUFACTURE OF CEMENT, PART 1 


J6 to 20 feet. In blasting, an effort is made to shatter the 
rock as much as possible in order to save subsequent sledging 
and blasting to break up the big pieces to a size that can be 
easily handled and crushed. 

In some quarries the rock is loaded on carts by hand and 
carried to a point out of danger from the blasting and dumped 
into side-dump cars which are hauled up an incline to the 
mill by a cable hoist. At other mills temporary tracks are 
laid from a turntable or switch at the foot of the incline to 
the rock piles; the cars are loaded directly from these and 
then hauled to the mill, as before. When the quarrying has 
been carried straight down the rock is loaded on skips that 
are hoisted up and carried to the mill by an aerial cable. 

Rock can be loaded much more cheaply with steam shovels 
than by hand and these are now used much in cement-mill 
quarries. To be successfully used, however, they require the 
installation of large crushers in the mill in order to crush the 
large stone which the steam shovel loads. 

65. Excavating 1 of Marl.— Marl carries considerable 
water and the deposits usually lie in depressions and under¬ 
neath the surface of a shallow lake or marsh. In excavating 
marl several plans are followed. One of the most common 
is to use a steam dredge mounted on a barge. The dredge 
scrapes up the marl from the bottom of the lake and loads 
it on barges. The barges are then towed to a wharf and 
unloaded by machinery, belt conveyers being used to carry 
the marl to the mill. Instead of using barges and cars for this 
purpose, the marl is sometimes dropped from the scoop of the 
dredge into the hopper of a pug mill on a boat or car. Here 
the marl is mixed with water to form a thin mud which is 
pumped to the mill through a pipe line carried over the marsh 
or marl bed on a wooden trestle. The dredges are of the same 
type as those used for deepening the channels of rivers and 
harbors. They consist of a scoop or dipper having a hinged 
bottom and fixed to a long arm. This arm can be swung to 
either side, raised, lowered, or pushed forward by a system of 
chains, racks, and pinions. The pug mill consists of a long 


MANUFACTURE OF CEMENT, PART 1 55 

steel cylinder in which two shafts provided with steel blades 
revolve. 1 he marl and water are fed in at one end and 
forced out at the other. During their passage they are 
churned up by .the blades and thoroughly mixed. 


MIXING PROCESSES 

66. Mixing: the Raw Materials. —In mills using the 
dry process the rock goes from the quarry to a stone house. 
Here it is treated in one of four ways: 

1. It is dumped directly into large piles and later subjected 
to analysis to determine how much limestone or clay must 
be added. After being weighed the rock is loaded on buggies, 
or barrows, and wheeled to the crusher where it meets another 
buggy, or barrow, loaded with the calculated amount of lime¬ 
stone or clay. The contents of the two barrows are then 
dumped into the crusher together or separately. 

2. The rock is weighed as it conies from the quarry and 
the proper amount of limestone or clay, as calculated from 
quarry analyses, is added. The contents of part of the cars 
are then dumped into the crusher and the contents of the other 
cars are dumped into a pile from which when necessary the 
material is wheeled to the crusher in barrows, etc. At several 
mills the contents of all the cars are dumped into the crusher, 
part of the crushed stone going to the mill and part of it being 
stored in bins for the night shift. The rock is drawn from the 
bins on belt conveyers running to the mill. 

3. The materials are crushed separately and stored in large 
bins the contents of which are analyzed. The materials are 
then mixed in proper proportions as determined by these 
analyses. This plan is followed at most of the plants using 
limestone and clay or shale. 

4. The materials are ground to a fineness of, say, from 10 to 
18 mesh, stored in separate bins of a capacity sufficient for 
6 hours or more, then analyzed and mixed accordingly. This 
is a particularly desirable way in the case of a clay-and-lime- 
stone mixture. The raw materials are weighed and then 
mixed during the grinding operation. 



56 


MANUFACTURE OF CEMENT, PART 1 



ing of steel cylinders generally 50 feet long and 5 feet in 
diameter. These driers are usually provided with angle irons 
bolted to the inside to act as shelves to carry the rock up and 


67. At some time during the mixing process the rock is 
usually dried. This is done in rotary driers, Fig. 11, consist- 





































































MANUFACTURE OF CEMENT, PART 1 


57 


expose it to the hot gases. Some of the cylinders have their 
upper half divided by means of plates into four compartments 
in order to expose a greater surface of rock. The driers are 
heated by a coal fire at the lower end. They are similar in 
construction to the rotary kiln previously described, except that 
they are not lined with firebrick. One drier 50 ft.X5 ft. will 
take care of 400 to 500 tons of rock in 24 hours. 

68. In the wet process the marl is usually received at the 
mill in the form of a thin mud. After removing roots, sticks, 
stones, etc., this mud is stored in large concrete basins or in 
steel tanks. The clay is dried, ground, and stored in bins. 
From the storage tank the marl is pumped either into a tank 
of known volume or into the hopper of a scale. The clay is 
then added as directed by the chemist. From the measuring 
tank or scales the mixture, or slurry, as it is called, is dumped 
into a pug mill and thoroughly mixed. From the pug mill 
the mass is run into large vats where it is sampled and analyzed. 
If of correct composition it is passed on for final grinding; if 
not, the required quantity of marl or of clay, as the case may 
be, is added. The vats are provided with stirrers to keep the 
mass in constant agitation to prevent the settling of any part 
of it and to mix in thoroughly any clay or marl that may be 
added to correct the mixture. Compressed air is used for 
agitating the contents of the slurry tanks and also revolving 
arms provided with paddles. In calculating the amount of' 
clay for marl or slurry, it is always necessary to find the 
percentage of water in the slurry and from this the amount of 
dry material in the vat. The amount of clay needed for this 
amount of dry slurry or marl is then calculated and added in 
the manner already explained in detail. 

Cement is also made from limestone and clay or shale by the 
wet process. In this -process the limestone and shale are 
handled as just described, and water is added just before the 
mixed materials are ground. If clay is employed in place of 
shale, it is usually mixed with water and reduced in a wash 
mill to a thin slip which is added to the limestone just before 
the latter is ground. It is claimed for the wet process when 


58 


MANUFACTURE OF CEMENT, PART 1 


applied to limestone and clay or shale that the grinding of the 
two materials is easier than in the dry process, and the drying 
operation is omitted. On the other hand, much more coal must 
be burned in the wet process than in the dry. 


GRINDING 

69. Grinding 1 the Raw Material. —Before burning it 
is necessary to grind the mixture of raw materials to a fine 
powder. Dry materials are usually ground in three stages 
{a, b, and c). 

(a) The first stage always consists in crushing the lime¬ 
stone or cement rock down to pieces 2 or 3 inches in size. 
This operation itself is usually done in two stages. A large 
crusher is employed to break the stone as received from the 
quarry, often in pieces a yard or more in size, down to about 
6 inches. This large crusher is then followed by smaller 
gyratory crushers or large hammer mills which reduce the stone 
to 3 inches and under, the size depending on the machinery 
employed in stage (b).* 

( b ) In this stage the material is reduced sufficiently to pass 
it on to the third stage (c). When tube mills are used for 
finishing the grinding it is necessary to reduce the material to 
20-mesh, but where Raymond mills, Griffin mills, or Fuller 
mills are employed for finishing it is necessary to reduce to 
only about 1 inch. In the latter event rolls or hammer mills 
are used in this stage. When the final grinding is done by 
means of tube mills the second stage grinding may be done by: 

(1) ball mills; (2) kominuters; (3) hammer mills; (4) Brad¬ 
ley Hercules; or (5) Griffin mills. 

(c) The final grinding may be done in: (1) Tube mills; 

(2) Griffin mills; (3) Fuller mills; and (4) Raymond mills. 
A combination ball and tube mill called a compeb mill is now 
employed to some extent and combines stages b and c in one 
operation. In the wet process as applied to limestone and 

*Note.—T he stone is usually dried after it passes through this 
crusher, and goes into storage. In the case of a limestone and clay 
plant, the mixing is often done while the rock is in this condition. 




MANUFACTURE OF CEMENT, PART 1 


59 


clay, or shale, the grinding is usually done in ball mills or 
kominuters followed by tube mills, or else by compeb mills 
alone. No drying is necessary. 

Opinions differ greatly as to what combinations are most 
efficient. Some manufacturers prefer one and some another, 
and there are good points in all. Unquestionably, too, some 
combinations give better results in certain hands or on certain 
materials, etc., than do others. 

Wet materals—marl and clay—are in a more or less finely 
ground state when excavated and the grinding here becomes 
more of a mixing process. The clay is usually disintegrated 
in dry pans or edge-runner mills, and the mixture of clay 
and marl is merely passed through a tube mill and then 
burned. These mills are described in detail later. 

70. The degree of fineness to which the raw material 
should be ground depends largely on conditions. It may be 
said that as a general rule the raw material should never be 
ground coarser than will permit 90 per cent, of the material 
to pass through a 100-mesh sieve and that in most cases a fine¬ 
ness such that 95 to 9S per cent, will pass through the sieve is 
required to produce a sound cement. Fine grinding also 
lessens the quantity of coal required for burning. The fine¬ 
ness of the raw material should be tested at least once a day 
and, if possible, two or three times a day, in order to have 
a check on the work of the mills and to keep them up to 
standard. 

71. Crushers. —The crushers used in cement works are 
usually of the gyratory type, though the jaw or Blake crusher 
is used to some extent. Fig. 12 shows a section of a Gates 
gyratory crusher. On the spindle g is mounted a chilled-iron 
crushing head c. The hopper-shaped top shell h is lined with 
concave chilled plates. The crushing is done in the annular 
space between the chilled surfaces of the crushing head and 
liners. The spindle is held centrally in the spider at the top 
and at the bottom it passes loosely through an eccentric driven 
by bevel gears b to give the spindle a gyrating motion. Thus, 
one point in the annular space is wide, while a point opposite 



Fig. 12 


60 



































































































































MANUFACTURE OF CEMENT, PART 1 


61 


is narrow, and the crushing force is obtained on account of the 
head approaching and receding from the concave liners. 
Crushers of this type are made in a variety of sizes and require 
from 1 to 1.2 horsepower per ton of rock crushed per hour, 
depending on the hardness of the rock. 

72. Large jaw crushers are now used to some extent for 
breaking down the rock as it comes from the quarry. These 
have the advantage that they will take a larger piece of rock 
than will a gyratory of the same capacity and hence are desir¬ 
able where steam shovels are used in the quarry and it is 
desired to keep the cost of the crushing plant low. Jaw 



Fig. 13 


crushers do not have as great capacity as the gyratory 
crushers, however, and are more easily clogged by means of 
clay in the rock. The jaw crusher, Fig. 13, as its name implies, 
consists of a swinging jaw a, which alternately approaches and 
recedes from a stationary jaw b fixed to the frame of the 
machine. The movement of the jaw is brought about by 
means of what is known as a pitman c, two toggles d, and an 
eccentric c. It will be readily seen from a reference to Fig. 13 
that as the eccentric raises the pitman the toggles straighten 
out and force the movable jaw nearer the fixed one, etc. The 
size of jaw crushers usually employed in cement mills have 


386—5 
































































62 


MANUFACTURE OF CEMENT, PART 1 


openings GO in.X48 in. and 84 in.XGO in. They require the 
same power to operate as a gyratory crusher. 

73. Griffin Mill.—The Griffin mill, which is shown in 
Fig. 14, though more complicated and consisting of a greater 



Fig. 14 


number of parts than either ball or tube mills, is admirably 
adapted to grinding or pulverizing both raw stone and clinker. 
It consists of a shaft a vertically suspended by a universal joint 
























































































MANUFACTURE OF CEMENT, PART 1 


63 


composed of a ball / with attached trunnions. The trunnions 
work in half boxes that slide up and down in recesses in the 
pulley-head casting. The shaft is driven by the pulley j. At 
the bottom of the shaft will be seen a fan g that draws in air 
from the top of the cone li and throws finely pulverized mate¬ 
rial against the vertical screen b on its own level. Below this 
fan is a roll c. The body of the mill consists of a base, or 
pan, d, against which the roll revolves, coming in contact with 
the steel ring, or die, e. It is between these parts that the 
material is pulverized, the finer particles being driven through 
the screen and the coarser ones falling to the bottom of the 
pan, only to be stirred up again by the plows, or scoops, on the 
bottom of the roll and brought between the die and roll. Out¬ 
side of the die the base has a number of openings through 
which the pulverized material is led downwards to the screw 
conveyer i underneath. The screen that surrounds the pul¬ 
verizing chamber is of much coarser mesh than the delivered 
product; for instance, a lG-mesh screen delivers a product of 
which more than 90 per cent, will pass a 100-mesh screen. 

A Griffin mill of the size usually installed in Portland cement 
works will grind from 4 to 0 tons of rock or from 12 to 
15 barrels of-cement per hour, the amount varying with the 
hardness of the rock and the condition in which the mill is 
kept. In doing this work from 75 to SO horsepower will be 
consumed. 

74. The Bradley Hercules Mill. —The Bradley 
Hercules mill is a new mill developed by the makers of the 
Griffin mill. It is somewhat similar to the latter in principle. 
This mill has three rolls, however, instead of one and is much 
larger than the Griffin mill. The rolls are suspended by a 
suitable frame and bearings from a single central shaft to 
which is attached the driving pulley. The mill is provided with 
screens and fans which perform the same work as in the 
Griffin mill. These mills are used only as preliminary mills 
to tube mills, as they will take 2- to 3-inch material and reduce 
it to 20-mesh. They have a very large capacity. One mill 
under these conditions will grind 100-150 barrels of clinker, 


64 


MANUFACTURE OF CEMENT, PART 1 


or 30 to 40 tons of raw material per hour and requires 
200-250 horsepower. 

75. Ball Mills. — Figs. 15 and 1G show two views of a 
ball mill that consists of a steel drum about S feet in diameter 



Fig. 15 


and 4 feet wide, the inner surfaces of which are lined with 
heavy plates of tough, hard steel. The drum revolves on a 
central shaft and carries with it part way round a number of 
steel balls c that by means of a series of offsets, or steps, h in 




























































































































































MANUFACTURE OF CEMENT, PART 1 


65 


the grinding plates are made to roll or fall on the material to 
be crushed. At each of the offsets is a slot, or opening, for 
the return of material to the mill. The grinding plates b are 
perforated, and the balls grind, or force, material through to 
the outside where it works its way to a series of screens e 
and p that separate the fine particles by allowing them to pass 
to the outer casing and drop to the hopper below while the 
coarser particles are re¬ 
turned to the mill through 
slots, or return channels, 
by scoop plates d for 
further reduction. The 
fineness of the grinding 
is regulated by the outer 
screen e, which is usually 
from 12 to 20 meshes per 
linear inch. This screen 
is attached to the rim a 
by setscrews. The coarser 
and inner screen p is made 
of perforated metal plates 
and is bolted to the rim k. 

A ball mill usually re¬ 
quires from 30 to 40 
horsepower and turns out 
4 to G tons of raw material 
and 12 to 16 barrels of 
clinker per hour. The 
balls vary from 3 to 5 
inches in diameter, and the 
charge of balls for a mill of the above size weighs about 1J tons. 

A modification of the ball mill in which no screens or per¬ 
forated plates are used, consists of a short tube mill lined with 
corrugated chilled iron plates and charged with large steel 
balls. The material is fed in through a hollow shaft at one 
end and works its way out through one at the other. 1 he fine¬ 

ness, as in tube-mill grinding, is regulated by the feed. A few 
cement plants have these ball mills. 























66 


MANUFACTURE OF CEMENT, PART 1 


76. Kominuter.— A modification of the ball mill hav¬ 
ing about double the capacity of that shown in Fig. 16, is 
known as the kominuter. It consists of a drum of nearly the 
same diameter as a ball mill, but of about twice its length. 
In action it differs from the ball mill chiefly in that the grind¬ 
ing plates are not perforated. Therefore the material does 
not fall out through the screens at once, but travels through 
the full length of the drum and passes on to a perforated 
plate screen through openings at the opposite end. The par¬ 
ticles that are too large to pass through this screen are returned 
automatically to the interior of the mill by means of buckets 
and S-shaped pipes. The material passing the inside screen is 
caught on the outside screen of wire cloth and further separa¬ 
tion efifected, the coarse material being returned to the mill 
as before. 

77. Tube Mill.— The tube mill shown in Fig. 17 con¬ 
sists of a cylinder of boiler plate, usually 5 to 7 feet in 
diameter and 20 to 22 feet long, suspended on trunnions, or 
bearings, at either end and rotating about a horizontal axis. 
The cylinder is lined with flint or trap-rock blocks cemented 
in, or with tough cast steel or other metal plates, and is filled 
to about half its capacity with hard Greenland or Danish flint 
pebbles varying from 1 to 3 inches in diameter. By a screw 
conveyer arrangement at one end material is fed in and dis¬ 
charged at points lying in either the axis or the perimeter of 
the cylinder. The material to be pulverized is fed in at one 
end and works its way toward the other while the mill is kept 
constantly rotating at a rate of 25 to 28 revolutions per minute. 
The tumbling of the pebbles on one another, with the material 
to be ground forming the bed in which they roll, causes the 
fine pulverizing action of the mill. The fineness is regulated 
by a device at the feed-end of the mill. This device can be set 
to control the amount of material entering and this in turn 
regulates the speed of material passing through and, conse¬ 
quently, the resulting fineness. By using this mill, a material 
of which 98 per cent, will pass a 100-mesh screen can easily be 
obtained. 



67 


Fig. 17 

























































































































68 


MANUFACTURE OF CEMENT, PART 1 


78 . It is now quite common practice to replace part and 
sometimes all of the pebbles by small steel balls or slugs. 
These slugs are usually about 1 inch long and J inch in diameter. 
When only part of the charge is of slugs a compartment is 
usually provided at the discharge end of the mill, and this is 
filled half full of slugs. The use of these slugs increases 
both the output and power consumption of the mill, but the 
increase in output is greater than in power consumption. The 
slugs also increase the fineness of the product. 

The capacity of a tube mill will depend on its size, the fine¬ 
ness and hardness of the material fed into it and of the 
product, the nature of the grinding medium, etc. Table XI 
gives the output and power requirements of various-sized mills 


TABLE XI 

CAPACITY OF TUBE MILLS 


Size Mill 

Operating on Clinker 

Operating on Raw Material 

' Diam. 

Length 

Output 

Barrels per Hour 

H. P * 

Output 

Tons per hour 

H. P* 

5 ' 6 " 

22 ' 

20 

100 

6J 

100 

6 ' 0 " 

22 ' 

24 

120 

8 

120 

7 ' 0 " 

22 ' 

34 

165 

12 

165 


*About double this power is required momentarily in starting. 


receiving 20-mesh material of average hardness and grinding 
to 80 per cent, passing the No. 200 sieve. The mills are lined 
with silex blocks and charged with pebbles. 

The use of a 5-foot compartment on any of the above mills 
charged with slugs will increase the capacity about 40 per 
cent, and the power necessary to operate by about 25 per cent. 

79 . Fuller-Lehigh Mill. —The mill shown in Fig. 18 
is a Fuller-Lehigh mill in which the grinding is done by means 
of a die a, and four balls b which revolve against it or rather 
are pushed around by four equidistant arms, or pushers, c 
(shown dotted behind the ball) radiating from a central 
vertical shaft d. The latter revolves at a speed of 130 to 




















MANUFACTURE OF CEMENT, PART 1 


69 


160 revolutions per minute, depending on the size of the mill, 
and the balls are pressed against the die by centrifugal force. 



ifi 

f= 

o 


zr 

T 

T 

’ 1 

i* 



m 


^ (Qi - fQi fQi 


1 


m 




% 


mmm. 


Fig. 18 


The material that is ground is fed in at e and eventually falls 
between the die and balls. There are fans f lt f 2 attached to 












































































































































































































































70 


MANUFACTURE OF CEMENT, PART 1 


the central shaft and these suck the fully ground material 
away from the coarser particles and blow it out through a set 
of screens g 1} g 2 around the upper part of the grinding chamber. 



Fig. 19 


The fineness is controlled by the mesh of the outer screen g 2 , 
and by the rate at which the material is fed into the mill. 

The Fuller-Lehigh mill is made in several sizes, those most 
used in cement mills being 42-inch and 54-inch, this dimension 
referring to the diameter of the die. The 42-inch mill will 





































































































































MANUFACTURE OF CEMENT, PART 1 


71 


require about 75 horsepower and will pulverize from 4 to 
5 tons of raw material or from 8 to 10 barrels of clinker 
per hour. The 54-inch mill will pulverize from 8 to 10 tons 
of raw material or 15 to 20 barrels of cement and requires 
125 horsepower. 

80. Raymond Mill. —The Raymond mill shown in 
Fig. 19 consists of three parts: a grinding unit A, a fan B, 
and a collector C. The grinding unit consists of a die a against 
which four or five rolls b revolve. These rolls are suspended 
from a spider c which is rotated by a central shaft. When 
the shaft revolves the rolls swing out against the die. Above 
the die is an air separator whose function is so to control the 
air-currents as to regulate the fineness of the product. The 



fan B draws the air through the mill and separator, the latter 
separates the fine material from the coarse and returns the 
coarse particles to the mill for further grinding. The fine 
material is carried off by the air, passes through the fan and 
is discharged into a cyclone collector where the ground material 
is deposited and the air returned to the mill. 

The Raymond mill is made into two sizes: four rollers and 
five rollers. It is suitable for grinding raw material and coal, 
but not clinker. The four-roller mill will grind about 4 tons 
of either raw material or coal to a fineness of 96 per cent, 
passing the No. 100 sieve and requires about 75 horsepower.. 
The five-roller mill has a capacity of 25 per cent, greater than 
the four-roller mill and requires about 90 horsepower. 





























































































72 


MANUFACTURE OF CEMENT, PART 1 


81. The Hammer Mill. —This mill is made by numerous 
machinery manufacturers, and while there are a number of 
different modifications of the type, they all consist essentially 
of a number of hinged hammers which revolve around a 
central shaft inside of a steel case. The hammers crush the 
material and it passes out through a grid screen as shown in 
Fig. 20. 

Large hammer mills are sometimes used to crush limestone 
to 2 inches, displacing the small gyratory crushers used in 
some plants for this purpose. They are most frequently used, 
however, after these crushers for the preparation of raw 
material for Fuller-Lehigh and Griffin mills, reducing in this 
case to i inch and are preferred to rolls for this purpose. They 
are used less frequently in connection with outside screens to 
prepare material for the tube mill, grinding in this case to 
20-mesh. They are also much used for crushing shale, but are 
not suitable for crushing clinker. 

These mills vary greatly in size and may be obtained of 
almost any desired capacity. When crushing from 3 to J inch 
they require about 2 horsepower per ton per hour of output 
—that is, a mill grinding 20 tons per hour will require 
40 horsepower. 

82. Ring Roll Mills. —There are two makes of ring roll 
mills, which are used to a limited extent for grinding clinker, 
namely, the Sturtevant and the Maxecon. Mills of this type 
consist of a vertical die against which three rolls revolve, and 
the grinding is done between the die and rolls. There is no 
screening device in the mill itself, but the separation of the 
fully ground and coarse material is done by an outside device. 
Either air separators or shaking or vibrating screens may be 
used for this purpose. 

83. Devices Used for Conveying Material in Mills. 

The material used in the manufacture of cement is usually 
conveyed from one part of the mill to another by mechanical 
means. The product of the Gates crusher is carried to the 
ball-mill bins or to the rolls on belt conveyers or scraper 
conveyers, and the fine material from the ball mills, Griffin 


MANUFACTURE OF CEMENT, PART 1 


73 


mills, and the tube mills is conveyed by means of screw con¬ 
veyers. The elevating is done by bucket elevators of the link- 
belt form. Slurry and marl are pumped by means of either 
the compressed-air system or a plunger pump of special design. 
Dry material is stored in steel bins at every stage of the 
process in order to have a constant supply for each unit of the 
grinding system, and marl and slurry are stored in concrete 
vats or steel tanks and kept in constant motion to prevent the 
heavier and sandy portions from settling. 


BURNING PROCESS AND APPARATUS 

84. Burning the Cement Mixture.— Saylor burned 
his first cement in upright kilns and the first mills in the 
United States used this form of kiln, which is still employed 
extensively in Europe. It necessitated the molding of the 
dry powder into bricks which were then dried and burned. 
Saylor used Portland cement as a binding material in the 
making of his bricks and at the American Cement Company’s 
plant coal tar was used, thus doing away with the preliminary 
drying. In 1885 Ransome obtained a patent in England for 
burning cement in a revolving furnace. The (experiment, 
however, proved a failure. In the United States a small plant 
in Oregon also tried to use the Ransome kiln and failed. 
About the same time the Atlas Portland Cement Company was 
formed and experiments with Ransome’s kiln were begun at 
first in New York and later with success on the cement rock 
of the Lehigh Valley. 

At first many difficulties were encountered and it was only 
after the raw material had been ground to an impalpable 
powder and moistened with water just before introduction into 
the kiln, that the process became satisfactory. At first the 
kilns were only 40 feet in length, but it was found more 
economical to increase the length to 60 feet. Crude oil was 
used for heating the kiln, the oil being bloAn into the kiln in 
the form of a spray. About the year 1898 powdered coal was 
introduced as fuel. The practice of moistening the finely 
ground raw material has been discontinued. 



74 


MANUFACTURE OF CEMENT, PART 1 


85. Rotary Kiln.— The rotary kiln, which consists of a 
cylinder made of steel plates bolted together and lined with 
firebrick, is now universally used in the United States. The 
length varies from 60 to 250 feet and the diameter of the 
shell varies from 6 to 12 feet. Formerly kilns were 6 feet 
in diameter and 60 feet long, but now they are generally 8 feet 
in diameter and 125 feet long. Kilns are made much larger 
than this, however, and those measuring 10 feet diameter and 
175 feet long are not uncommon, the kilns being made longer as 
their diameter is increased. They revolve on two or, in some 
cases, more tires resting on idlers, and are turned by a gear and 
pinion. The upper end of the kiln projects just inside a short 
brick flue called the dust chamber, which is in turn surmounted 
by a steel stack. The lower end of the kiln is closed by a 
movable firebrick hood. The raw material is held in a large 
steel bin and is introduced into the upper end of the kiln by 
means of either a screw conveyer working in a water-jacketed 
case, or else by an inclined cast-iron spout. 

The kiln is slightly inclined and as it revolves the material 
works down toward the burning coal. The first change that 
takes place is the driving ofif of the moisture, then the powder 
begins to lose its carbon dioxide and to form into small, soft, 
yellow balls; finally, as they work their way down into the 
hottest part of the kiln, these balls are partly vitrified or 
clinkered and change to a greenish-black color. The clinker is 
then burned and drops from the mouth of the kiln through 
an opening in the hood into either a clinker pit, a rotary cooler, 
or an elevator that conveys it to an upright cooler. 

The inclination of the kiln varies with its size. Small kilns 
6 to 7 feet in diameter are usually pitched at an angle of J inch 
per foot to the horizontal, while larger kilns are usually 
inclined \ to § inch to the foot. The firebrick lining is usually 
9 inches thick in the burning zone and 6 inches in the upper 
part of the kiln. The brick are made to fit the kiln radius 
and are of high alumina clay. Sometimes a layer of some 
heat-insulating material such as sil-o-cel is placed in the upper 
part of the kiln between the firebrick and the shell in order to 
conserve the heat. 


75 


MANUFACTURE OF CEMENT, PART 1 

The raw material is fed out of the bin in which it is stored, 
by means of a screw conveyer. This is driven from the kiln 
shaft so that when the kiln stops revolving the feed stops. 
Kilns are now usually driven by means of variable-speed 
motors. When the material burns readily the kilns are 
operated at their highest speed, but when the fuel fails to burn 
properly the speed is decreased, allowing the material to remain 
in the kiln a longer time and giving the heat more time to act 
upon them. 

The slurry of the wet process is fed directly into the kiln 
without any preliminary drying. In wet burning the upper 


TABLE XII 

AVERAGE CAPACITY OF ROTARY KILNS 


Size 

Dry Process 

Wet Process 

Diam¬ 

eter 

Feet 

Length 

Feet 

Output 
Barrels per 
Day 

Coal per Barrel 
Pounds 

Output 

Barrels per 
Day 

Coal per Barrel 
Pounds 

6 

60 

200 

110 

140 

150 

7 

100 

400 

95 

300 

135 

8 

125 

650 

90 

450 

120 

9 

150 

1,000 

88 

700 

115 

10 

175 

1,300 

85 

900 

110 - 


50 to 75 feet of the kiln serves to evaporate the water, but from 
this point on the action in the wet and dry processes is alike. 


80. The output and coal consumption of rotary kilns vary 
with the size of the kilns. Some materials also burn more 
readily than others. Table XII gives the capacity and fuel 
consumption of various-sized kilns. As will be seen, the long 
kilns not only give greater output but use less coal. This is 
due to the fact that the lengthening of the kiln keeps the raw 
material in contact with the hot gases for a longer time and 
consequently allows the raw material to extract the heat from 
the hot gases better. The wet process takes about one-third 
more fuel than the dry. 
























76 


MANUFACTURE OF CEMENT, PART 1 


The ordinary rotary kiln is very wasteful of fuel, its 
efficiency not being more than 20 per cent. The distribution 
of fuel is about as follows: p c ENT 


Employed in decomposing raw materials and 


forming clinker . 20 

Heat carried off by the stack gases. 41 

Heat carried off by the clinker. 17 

Loss due to radiation, etc. 22 

Total . 100 


i 


87. Fuel. —Coal is generally used as a fuel for the kilns, 
but natural gas and oil are used in localities where they are 
cheaper than coal, the choice of fuel being purely a matter of 
economy. Bituminous coal as high in volatile matter as can 
be obtained cheaply is preferable. It should be pulverized so 
finely that at least 90 per cent, of it will pass the No. 100 
sieve. 

The coal is first run through a set of rolls or a pot cracker to 
reduce it to 1 inch and under. It is then dried in special forms 
of rotary driers in which the coal is not heated to the point 
where combustion or even loss of volatile combustible matter 
can take place. This is accomplished by allowing the gases 
from the coal fire to cool somewhat before they are passed over 
the coal to be dried. Different types of driers secure this 
result by different means, but in one type commonly employed 
the result is obtained by enclosing part of the cylinder in the 
brickwork of the firebox. The coal is thus heated first by the 
gases from without which are also cooled to a point which will 
allow them to be brought in contact with the coal. They are 
then led into the cylinder by means of a suitable flue. The coal 
is pulverized in either Raymond or Fuller-Lehigh mills. A few 
of the older plants employ either Griffin mills, or ball-and- 
tube mills. 

The powdered coal is stored in a bin in front of the kiln and 
fed out of this by means of a screw conveyer, the speed of 
which can be controlled by some appropriate device so as to 
give any amount of coal desired. The coal falls from this 
feed into an injector by means of which it is blown into the 








MANUFACTURE OF CEMENT, PART 1 77 

kiln, air being supplied by means of a fan at about 6 to 
10 ounces pressure. 


The coal and-air pipe leads just into the kiln and the coal 
takes fire a few feet from the end of this pipe, burning with a 



luminous flame not unlike that of a large blow torch. Only 
a part of the air necessary for combustion is blown in, the 


386—6 




























































78 


MANUFACTURE OF CEMENT, PART 1 


balance being sucked in through various openings at the front 
of the kiln. 

88. A battery of ten kilns is shown in Fig. 21, in which 
A is the kiln, b the brick-dust chamber, c the stack, D the raw- 
material boxes, e the hood, f the coal pipe to carry the coal 
into the kiln, F the coal boxes, and G the fan for supplying 
air. 

89. Chemical Changes During Burning.— The 

changes that take place during burning may be summed up 
as follows: 

The carbon dioxide existing in the raw material in com¬ 
bination with the calcium and magnesia as carbonates of these 
elements is practically entirely expelled. 

All the water originally present, whether free, hygroscopic, 
or combined, is driven off and the carbon and organic matter 
in the raw material are also burned away. The iron, the 
greater part of which is usually present in clay and cement 
rock in the ferrous condition, is almost completely oxidized. 

Most of the sulphur, whether present in the raw material as 
sulphide, sulphate, or in combination with organic matter, is 
expelled, all the remainder except a mere trace usually being 
calcium sulphate. The alkalies, potash and soda, are partly 
expelled in the kiln. Some experiments have shown losses of 
soda amounting to 19 to 28 per cent., while the loss of potash 
ran from 46 to 52 per cent. 

The changes here mentioned are those which can be detected 
by chemical analysis. In addition to these certain combina¬ 
tions take place the most important of which is the union of 
lime with the silica and alumina to form tricalcium silicate and 
tricalcium aluminate, respectively, and this union takes place 
only when the mixture vitrifies or clinkers. 

Of these chemical changes the driving off of the water and 
the carbon dioxide are endothermic, so called because they 
require that heat shall be supplied to bring the changes about, 
while the burning of the organic matter and the combination 
of the silica and the alumina with the lime are called exothermic 
because they give off heat. The difference between these 


MANUFACTURE OF CEMENT, PART 1 


79 


reactions amounts to 580 B. T. U. per pound of clinker or about 
220,000 B. T. U. per barrel. The latter figure is equivalent to 
15J pounds of good coal (14,000 B. T. U. per pound). This is 
much below the amount of fuel actually used and the differ¬ 
ence between the heat required and that used is lost by the heat 
in the clinker and in the stack gases and by radiation from 
the kiln shell as already explained. 

90. Degree of Burning.— Properly burned Portland 
cement clinker is greenish-black in color, of a vitreous luster, 
and, when just cooled, usually sparkles with little, bright, 
glistening specks. It forms in lumps from the size of a wal¬ 
nut down, with here and there a larger lump. Underburned 
clinker, due either to a low temperature in the kilns or to an 
overlimed mixture, lacks the vitreous luster and the glistening 
specks. The failure to sparkle, however, is not necessarily 
characteristic of underburned clinker, though the sparkle itself 
is never seen in underburned clinker, as the rate of cooling, 
etc., affects the appearance of sparkle somewhat. If much 
underburned, the clinker is brown, or has soft brown or yellow 
centers. Clinker low in lime, unless very carefully burned, 
usually has brown centers also, but the centers are hard and 
thoroughly vitrified. 

There is probably a relation between fineness, time in the 
burning zone, and temperature of the kiln. It is a well-known 
fact that fine materials require less time for burning or a 
lower temperature than do coarser ones. Likewise less time 
is required in a high temperature than is needed in a lower 
one, etc. The composition also affects all three of these con¬ 
ditions. High-lime cements require higher temperatures, finer 
grinding, or longer time in the kiln than do low-lime cements. 
It is understood that varying one condition may call for a 
change in the others. The time of burning is controlled by 
slowing the speed of the kiln or by lengthening the hot zone, 
which is brought about by cutting down the draft. The actual 
temperature of cement kilns as measured by optical pyrom¬ 
eters does not seem to vary widely and ranges between 2,300° 
F. and 2,000° F. 


80 


MANUFACTURE OF CEMENT, PART 1 


91. Waste Heat Recovery.— As previously explained, 
about 40 per cent, of the fuel supplied to the kiln is represented 
in the heat of the waste gases. The latter leave a dry-process 
kiln at a temperature of from 1,500° F. to 1,800° F. and a wet- 
process kiln at a temperature a few hundred degrees lower. It 
has recently been found that by drawing the gases from the 
kilns through water-tube boilers a considerable amount of heat 
contained in the waste gases could be recovered. The boilers 
are connected to the dust chamber by means of a short flue and 
the gases are drawn through the boiler by means of a draft fan, 
care being exercised to prevent entrance of cold air. Usually 
an economizer is placed after the boiler to utilize still further 
the heat in the gases by heating the feedwater for the boiler. 
The heat utilized by such a waste-heat boiler system amounts in 
the case of a dry-process plant to about 11^ boiler horsepower 
hours per barrel of cement produced. With modern steam 
turbines directly connected to electric generators enough power 
is provided to operate the entire cement plant. 

92. Dust From Cement Kilns.— Normally in the dry 
process from 3 to 5 per cent., and in the wet process possibly 
a little less, of the raw material is carried out of the kilns by 
waste gases. This is the finest portion of the material and it is 
often transported by the winds and air a considerable distance 
from the plant and deposited on the surrounding country. 
Occasionally complaints have been made on account of this 
dust, particularly when the mills have been located in rich 
agricultural communities or near cities and towns. 

It has in some cases, therefore, been necessary to collect this 
dust in order to prevent its becoming a nuisance to the people 
living near the plants. Two methods have been devised for col¬ 
lecting the dust: (1) by means of water sprays, and (2) by 
electrical precipitation (Cottrell system). .In the former the 
gases are led through long chambers in which they are thor¬ 
oughly washed by means of water sprays, the drops of water 
carrying down the dust. In the latter the gases are passed 
through a large number of iron pipes through the center of 
each of which an iron wire passes. The-pipe and wire are 


MANUFACTURE OF CEMENT, PART 1 


81 


connected to the terminals of a high-potential (45,000 to 
80,000 volts) direct electric current. There is a silent dis¬ 
charge of electricity from the wire to the tube, and the effect 
of this is to precipitate the dust, the larger portion collecting 
on the tube. At stated intervals the flow of current is inter¬ 
rupted and the dust rapped off the pipe into hoppers located 
below. 

93. Potash Recovery.— Attention has already been 
called to the volatilization of potash from the raw materials 
during burning. This amounts on an average to about 
2 pounds of K 2 0 for every barrel of cement burned. By either 
of the two methods mentioned a considerable proportion of this 
potash can be recovered. In the case of the water spray sys¬ 
tem the potash goes into solution and may be recovered by 
evaporation from the water in the form of sulphate. In the 
case of the electrical precipitation method, the dust may be 
leached with water, when the potash will go into solution. The 
latter is filtered from the solid matter and the potash recovered 
as above stated. The dust itself contains from 3 to 10 per cent, 
of potash, depending on the amount in the raw materials, 
efficiency of the recovery apparatus, etc. As it also contains 
considerable lime, the dust has real value as a potash-lime 
fertilizer and can be sold for this purpose. If salt is added to 
the raw materials the amount of potash volatilized is increased, 
and, incidentally, the dust collected will be richer in potash. 
During the war when potash could not be obtained from Ger¬ 
many, the world’s source of supply, potash was collected and 
sold at a profit at a number of cement mills. With the return 
of the German supply the extraction of potash from the dust 
was not so profitable. Neither is it always possible to make 
good cement from the dust recovered and most attempts to 
use it so have failed. It is highly desirable, therefore, where 
dust must be collected to find a local market for this very 
valuable potash-lime fertilizer. 

94. Cooling- the Clinker.— The clinker is usually at a 
temperature of 1,800° F. to 2,000° F. when it leaves the kiln. 
It is almost the universal practice to spray it with water just 


82 


MANUFACTURE OF CEMENT, PART 1 


as it leaves the kiln. This not only cools the clinker but also 
seems to fix its chemical composition better. Formerly the 
upright cooler, which consists of an upright sheet-iron 
cylinder about 8 ft.X35 ft., was used extensively to cool the 
clinker. The cylinder is provided with baffle plates and 
shelves, and when the clinker falls over these, it is exposed 
to a current of air blown in by a fan and cooled. Revolving 
coolers are also used. These consist of a cylinder similar in 
construction to a kiln except that they are smaller and unlined. 
A cooler for an 8 ft.Xl25 ft. kiln is usually 5 feet in diameter 
and 50 feet long. The coolers are pitched at an angle and 
the clinker falls directly from the kiln into the upper end and 
works its way through. A current of air is sucked through the 
cooler by means of the kiln draft passing into the kiln. These 
coolers, therefore, serve not only to cool the clinker but also 
to preheat the air for combustion, and so effect an economy in 
operation. Many of the newer mills do not employ a grab 
bucket and crane to handle the clinker, but cool their clinker 
in piles with the help of water. 

It is now the general practice before grinding to season the 
clinker by allowing it to remain in large piles exposed to the 
weather for a period of 4 to 6 weeks, and even much longer. It 
has been found that clinker so seasoned not only grinds easier 
but cement made from it is more apt to be sound and have 
correct setting properties. The seasoning no doubt causes the 
slaking of the free lime present and this in turn breaks down 
the structure of the material. The mixing of a large quantity 
of clinker burned at different times also promotes uniformity 
of the product. The clinker is usually handled in and out of 
storage either by means of a system of conveyers over and 
under the pile or else by a grab bucket and overhead or 
locomotive crane. 

95. Grinding- the Clinker. —After cooling, the clinker 
is ground by one of the following systems: 

1. Tube mill preceded by: (a) ball mill; (b) kominuter; 
(c) Griffin mill; (d) Hercules mill, Maxecon mill; (e) Sturte- 
vant mill. 


MANUFACTURE OF CEMENT, PART 1 


83 


2. Griffin mill preceded by: ( a ) ball mill provided with per¬ 
forated plates and without screens; ( b ) crushing rolls; (c) pot 
cracker. 

3. Fuller mill preceded by same equipment as given above 
for Griffin mill. 

4. Sturtevant mill, preceded by: ( a ) crushing rolls; or 
( b ) pot cracker, followed by (c) screen; or (d) air separator. 

5. Maxecon mill, preceded by: (a) crushing rolls; or 
(b) pot cracker, followed by (c) screens; or ( d ) air separator. 

In order to regulate the set of the cement it is necessary to 
add sulphuric acid in some form or other, usually in the form 
of gypsum. This can be most readily done before grinding, 
insuring a thorough mixing. When cement becomes quick¬ 
setting on storage, it can often be made slow-setting by addition 
of finely ground plaster of Paris. This is usually done by 
adding at regular intervals a quantity of plaster to the cement 
as it is being carried from the stock-house bins to the packers. 
The conveyer does the mixing. 

96. Storage of Cement. —From the clinker mills the 
cement is conveyed to the stock house. At the older plants 
this is a long, low frame building provided with wooden bins. 
The cement is brought in by an overhead screw conveyer and 
dropped into the proper bin by means of slides and spouts. A 
screw conveyer runs along either the center of the stock house 
with bins on each side or along each side of the stock house 
with the bins in the middle. When a bin is to be opened for 
packing, the sideboards are removed and the cement is allowed 
to run into the conveyer freely as long as it will. When the 
cement ceases to run freely, it must either be pulled to the con¬ 
veyer by means of a long-handled scraper having a broad blade 
or else put into barrows and wheeled to the conveyer. The 
screw conveyer conducts the material to the packing machines. 

A more modern adaptation of this old stock house has con¬ 
crete side walls and either frame or concrete partitions between 
the bins. The conveyers are in tunnels running underneath 
bins which have sloping bottoms. This arrangement allows 
the cement to be drawn out of the bins and into the conveyer by 


84 


MANUFACTURE OF CEMENT, PART 1 


gravity. The most recent type of stock house is shown in 
Fig. 22 and is built on the order of a grain elevator with high 
reinforced-concrete tanks or silos for bins. These bins are 
usually 20 to 25 feet in diameter and 50 to 80 feet tall. 







■ •'id/- 


Fig. 22 


Tunnels containing the conveyers run under the silos and 
permit the silos to be emptied almost completely. The advan¬ 
tages of this type of stock house over the older ones are: cheap¬ 
ness to build, compactness, and the thoroughness with which the 
bins can be emptied without resorting to manual labor. 


PACKING CEMENT 

07. Cement is usually packed into paper or cloth bags. It 
is rarely packed in barrels, although the barrel is still con¬ 
sidered the standard unit of quantity and consists of 376 pounds 
net. There are four sacks to the barrel, and each bag contains 
94 pounds net. Barrels are packed by means of machines 
similar to those used for packing flour, and occasionally sacks 
are also packed in the same way. 

Almost all cement is now put into bags by the Bates system. 
This system depends upon a novel bag, the fundamental feature 






































































MANUFACTURE OF CEMENT, PART 1 


85 


of which is a valve in one corner. This is made by turning 
down and sewing in one corner. When pressure is applied to 
this valve, as when cement comes against it, the valve closes. 
With this bag the order of filling is reversed and the bag is first 
tied by means of a wire tie and then filled through the valve. 
The machine used for filling is provided with three or four 
tubes. The valve of the bag is slipped over one of these tubes, 
a gate is opened, and cement is forced through the tube into the 
bag. As the bag fills, it rests on a cradle. When the desired 
weight of cement is in the bag, the cradle, which is balanced by 
weights, falls and cuts off the flow of cement. The attendant 
merely slips the bag on the tube, starts the flow of cement, 
and removes the sack when full. Otherwise the operation is 
automatic. 

Very little cement is now packed in wooden barrels and only 
for export trade. The cement is packed just as it is about to 
be shipped, and the bags or barrels are trucked directly to the 
cars. For this reason the packing room should be arranged so 
that the cars to be loaded can be brought alongside of the room, 
and a shed roof is run out over the cars so that the loading will 
not be interrupted by rainy weather. The floor of the packing 
room should be level with the floor of the cars to be loaded. 

Cloth bags are used more than anything else for the packing 
of cement. The consumer is charged a fixed sum for the bag 
and is allowed a credit of the same amount for it when it is 
returned. All bags are marked with the label of the brand, so 
that each manufacturer knows his own bags. Barrels and 
paper bags are sold to the customer and are not returnable. 


POWER PLANT 

98. The balance of the equipment of a cement plant is 
similar to that of metallurgical and chemical plants. A large 
quantity of power is required in grinding the raw materials 
and the hard clinker. The power plant of a modern cement 
mill is, therefore, a large one. The size of the power plant 
will depend to some extent on the hardness of the raw 
material and on other considerations, but in general it may 



86 


MANUFACTURE OF CEMENT, PART 1 


be said that there will have to be provided 1 horsepower for 
each barrel of cement ground per day—that is, a 3,000-barrel- 
per-day cement plant will require about 3,000 horsepower. 
Roughly speaking, about two-thirds of this power is- required 
to grind the raw materials and the clinker, and the balance is 
used by the kilns and other machinery. 

All modern cement plants employ motor drives. In this sys¬ 
tem the power plant consists of either steam turbines or Corliss 
engines directly connected to powerful electric alternating- 
current generators, which furnish the current transmitted to 
various parts of the mill by copper cables. The machines are 
then driven by individual motors. In some cases the motors 
are directly connected to the machinery, but generally belts 
or chain drives are employed. The kilns are driven by vari¬ 
able-speed motors, and Fuller and Griffin mills are driven by 
vertical motors. Owing to the large amount of power 
required, the equipment must be first-class and carefully laid 
out. 


GENERAL CONSIDERATIONS 

99. Cement plants are no longer built in this country of a 
capacity smaller than 1,000 barrels per day, and generally the 
mills are from 2,500 to 3,000 barrels per day. There are a 
number of mills, however, which produce very much more than 
this quantity of cement. 

A modern Portland cement plant exclusive of the value of 
real estate, mineral deposits, stock of bags, working capital, 
etc., will cost about $2.25 per barrel of cement produced 
annually. In other words, a plant producing 3,000 barrels daily 
will make about 1,000,000 barrels annually and will cost about 
$2,250,000. In 1914, when conditions were considered normal, 
a cement plant cost about $1.00 per barrel of annual produc¬ 
tion. The cost of manufacturing cement varies with different 
localities, but was approximately $1.50 per barrel during the 
abnormal period of the war. During normal conditions, the 
cost per barrel of cement is approximately 75 cents. 



MANUFACTURE OF CEMENT 

Serial 2051B (PART 2) Edition 1 


TESTING OF PORTLAND CEMENT 


PHYSICAL TESTS 

1. Introduction. —Tests of cement may be classified as 
physical and chemical. The value of a cement is determined 
largely by physical tests, not only because in actual practice 
the cement is subjected to physical stresses, hut also because 
the value of cement depends not so much on the percentage 
of lime, silica, and alumina present, as on the thoroughness 
with which these have combined with one another. Moreover, 
physical testing does not require so much previous training as 
is necessary to fit one for making chemical analyses. It must 
not be inferred, however, simple as the directions may seem, 
that any one can become an expert physical tester in a few 
days. Time and practice only can make a skilful physical 
tester, as it has been repeatedly shown that the same cement 
in the hands of two different testers may give very widely 
differing results. In fact, some very high-grade cements have 
been condemned on many occasions, owing to a lack of experi¬ 
ence on the part of the tester, or because of the neglect of a 
skilful operator to observe some of the numerous precautions 
necessary to assure uniform results. 

2. All cement is tested under what are known as “the 
Standard Specifications and Tests for Portland Cement,” drawn 
up by a joint committee of the American Society for Testing 
Materials, the American Society of Civil Engineers, the Port- 


COPYRIGHTED BY INTERNATIONAL TEXTBOOK COMPANY. ALL RIGHTS RESERVED 




2 


MANUFACTURE OF CEMENT, PART 2 


land Cement Association, the United States Government, and 
other organizations. These specifications, as adopted in 1917, 
are as follows: 

STANDARD SPECIFICATIONS AND TESTS FOR PORTLAND 

CEMENT 

1. Portland cement is the product obtained by finely pulverizing clinker 
produced by calcining to incipient fusion an intimate and properly pro¬ 
portioned mixture of argillaceous and calcareous materials, with no addi¬ 
tions subsequent to calcination excepting water and calcined or uncalcined 
gypsum. 

I. Chemical Properties 

2. The following limits shall not be exceeded: 

Per Cent. 


Loss on ignition.4.00 

Insoluble residue .85 

Sulphuric anhydride (N0 3 ).2.00 

Magnesia ( MgO ).•.5.00 


II. Physical Properties 

3. The specific gravity of cement shall be not less than 3.10 (3.07 for 
white Portland cement). Should the test of cement as received fall 
below this requirement, a second test may be made upon an ignited 
sample. The specific gravity test will not be made unless specifically 
ordered. 

4. The residue on a standard No. 200 sieve shall not exceed 22 per 
cent, by weight. 

5. A pat of neat cement shall remain firm and hard, and show no 
signs of distortion, cracking, checking, or disintegration in the steam 
test for soundness. 

6. The cement shall not develop initial set in less than 45 minutes 
when the Vicat needle is used, or 60 minutes when the Gilmore needle 
is used. Final set shall be attained within 10 hours. 

7. The average tensile strength in pounds per square inch of not less 
than three standard mortar briquettes composed of one part cement and 
three parts standard sand by weight shall be equal to or higher than the 
following: 




Tensile Strength, 

Age 

Storage of Briquettes 

in Pounds 



per Square Inch 

7 days 

(1 day in moist air, 6 days in water). 

200 

28 days 

(1 day in moist air, 27 days in water). 

300 



















MANUFACTURE OF CEMENT, PART 2 


3 


8. The average tensile strength of standard mortar at 28 days shall 
be higher than the strength at 7 days. 

III. Packages, Marking, and Storage 

9. The cement shall be delivered in suitable bags or barrels with the 
brand and name of the manufacturer plainly marked thereon, unless 
shipped in bulk. A bag shall contain 94 pounds net. A barrel shall con¬ 
tain 376 pounds net. 

10. The cement shall be stored in such a manner as to permit easy 
access for proper inspection and identification of each shipment, and in a 

i 

suitable weather-tight building which will protect the cement from 
dampness. 

IV. Inspection 

11. Every facility shall be provided the purchaser for careful sampling 
and inspection at either the mill or at the site of the work, as may be 
specified by the purchaser. At least 10 days from the time of sampling 
shall be allowed for the completion of the 7-day test, and at least 31 
days shall be allowed for the completion of the 28-day test. The cement 
shall be tested in accordance with the methods hereinafter prescribed. 
The 28-day test shall be waived only when specifically so ordered. 

V. Rejection 

12. The cement may be rejected if it fails to meet any of the require¬ 
ments of these specifications. 

13. Cement shall not be rejected on account of failure to meet the 
fineness requirement if upon retest after drying at 100° C. for.l hour 
it meets this requirement. 

14. Cement failing to meet the test for soundness in steam may be 
accepted if it passes a retest, using a new sample at any time within -28 
days thereafter. 

15. Packages varying more than 5 per cent, from the specified weight, 
may be rejected; and if the average weight of packages in any shipment, 
as shown by weighing 50 packages taken at random, is less than that 
specified, the entire shipment may be rejected. 

3. Specific Gravity. —The test is designed to detect 
underburning and adulteration. Unfortunately for any con¬ 
clusions that might be drawn as to the latter, low specific gravity 
is often, and, indeed, is usually caused by aging or seasoning 
of the cement, so that to reject a cement because of a low 
specific gravity may be to reject it because it has been well 
seasoned. It is now generally acknowledged that cement is 
greatly improved by seasoning, as the water and carbon dioxide 


4 


MANUFACTURE OF CEMENT, PART 2 


absorbed from the air react with any free or loosely combined 
lime that might otherwise cause the cement to be unsound. As 
the cement absorbs these constituents from the air, its specific 
gravity becomes less' and less. The specific-gravity test is not 
of any value in detecting mixtures of natural cement and Port¬ 
land, sold as the latter, because some natural cements notably 
those from the Lehigh District in Pennsylvania have a specific 
gravity that is practically as high as that of Portland cement. 

The determination of the specific gravity of cement should 
always be made on a sample as received, but if the cement fails 
to pass the test a second trial may be made upon a sample 
ignited at a red heat. 

4. Detection of Adulteration. —Should the cement show 
a low specific gravity, the residue left by sieving from 100 to 
200 grams of the cement through a 100-mesh sieve should be 
examined under a low-power microscope or a pocket magnifier 
to see if the cement has been adulterated. Slag may be 
detected by its color and fracture, the former being bluish or 
white and the latter sharp and irregular, while Portland-cement 
clinker is almost black or dark brown and is in more or less 
rounded particles. Limestone and cement rock may be detected 
by their appearance and by effervescence with acids. The 
foreign particles may be picked out with a pair of fine tweezers 
and further identified by grinding fine in an agate mortar and 
analyzing. If the cement has been ground in tube mills the 
residue will also contain flint from the pebbles. This flint is 
not an adulteration and may be distinguished from slag be¬ 
cause, after grinding, its particles are insoluble in acid. Cements 
may also contain particles of iron from the Griffin mills or ball 
mills. These are magnetic and may be detected by this 
property. 

5. The Specific Gravity Test.— The method of con¬ 
ducting the test is as follows: Sixty-four grams of cement is 
carefully weighed on scales that should be sensitive to at least 
.005 gram. The flask, Fig. 1, is filled with kerosene free from 
water, or with benzine not lighter than 62° Baume, which have 
no action on the cement, to some point on the stem between the 


MANUFACTURE OF CEMENT, PART 2 


5 


zero and the 1-cubic-centimeter mark. The cement of the same 
temperature as the liquid is slowly introduced into the flask, 
care being taken that the cement does not adhere to the sides 
of the flask above the liquid and that all air bubbles are removed. 
After all of the cement has been 
introduced into the flask the level 
of the liquid will rise to some 
division of the graduated neck. 

The volume of liquid displaced 
by the 64 grams of cement is the 
difference between the initial and 
the final reading, and the spe¬ 
cific gravity of the cement is 64 
divided by that quantity. For 
example, suppose that the initial 
reading on the flask is .42 and 
that the final reading is 20.93; 
then the displaced volume will 
be 20.93 —.42 = 20.51 cubic centi¬ 
meters and the specific gravity 
will be 64-k20.51 = 3.12. 

The apparatus must be pro¬ 
tected from changes in tempera¬ 
ture while in use, because even 
touching the flask with the fin¬ 
gers will change the volume of 
the liquid noticeably. The flask 
should be immersed in water dur¬ 
ing tbe test to prevent variations 
in the temperature of the flask 
and contents. The variation in 
temperature should not exceed .5° C. (.9° F.) and the results 
of repeated tests should agree within .01. 

A convenient method of cleaning the apparatus is to invert 
the flask over a large vessel preferably a glass jar, and shake 
it vertically until the liquid begins to flow freely; it is then 
held still in a vertical position until empty. The remaining 
traces of cement can be removed in a similar manner by pour- 



































































6 


MANUFACTURE OF CEMENT, PART 2 


ing into the flask a small quantity of clean liquid and repeating 
the operation. 

t 

(>. Fineness.—The fineness of a cement is determined 
by sifting a sample through a 200-mesh sieve, or, in other words, 
a sieve having that number of meshes per linear inch. The 
size of each of the meshes nominally is .0029 inch, but the 
actual opening depends on the gauge of the wire. That for 
the 200-mesh sieve (No. 200) should be .0021 inch in diameter. 
The United States Bureau of Standards will measure and 
report on any sieve submitted to them and a sieve which has 
been passed by them should always be used if possible. Any 
sieve is considered standard which has between 192 and 208 
meshes and in which the diameter of the wire is between the 
outside limits of .0019 and .0023 inch. The cloth should be 
carefully placed in the frames so as not to stretch and distort 
the meshes. The frame itself should be of brass 8 inches in 
diameter and provided with a pan and cover. 

The standard method of making the tests is as follows: 
Exactly 50 grams - of cement (weighed on a balance sensible 
to at least .01 gram) is placed in the No. 200 sieve, which 
should be thoroughly clean and dry. The pan and cover should 
be attached to the sieve and the latter held in a slightly inclined 
position with one side about 1J to 2 inches lower than the 
other. The sieve in this position is moved rapidly back and 
forth at the rate of about 150 strokes per minute, at the same 
time gently striking the upper side against the palm of the 
other hand on the upward stroke. The sieve should be turned 
every twenty-five strokes about one-sixth of a revolution in the 
same direction, so as to make a complete revolution every 
minute. During the operation the cement should be kept as 
evenly distributed over the surface of the sieve as possible. The 
operation is continued until not more than .05 gram passes 
through the sieve in 1 minute of continuous sieving. 

Instead of using the pan and cover to the sieve, a good 
plan is to do the sieving over a sheet of clean paper or oilcloth 
and to take care that the cement is not bounced over the top 
of the sieve. When it is desired to ascertain whether or not 


MANUFACTURE OF CEMENT, PART 2 


7 


the operation has been completed, the material on the paper is 
rolled to one side by lifting the edge of the paper, thus expos¬ 
ing a clean surface over which the sifting may be continued and 
the amount passing through the sieve observed. An experi¬ 
enced operator will be able to tell by his eye and sense of time 
when the operation is finished without recourse to watch, bal¬ 
ance, and weights. 

The residue on the sieve is weighed. The fineness is then 
found by multiplying the weight of residue so found, by 100 
and dividing by the weight of cement taken. The result is 
reported as the residue on the No. 200 sieve. Of course, a 
simple way to calculate the percentage of residue when exactly 
50 grams of the sample is taken, is to multiply the weight of 
the residue in grams by 2. The houses supplying apparatus for 
cement-testing usually list very convenient little balances for 
fineness determinations in which the percentage of residue can 
be directly read ofif. 

Mechanical devices for sieving are on the market, but are 
not considered standard. They are, however, convenient, par¬ 
ticularly at the cement plant where many fineness determina¬ 
tions are made daily. Formerly cement was tested through a 
No. 100 sieve, also, but this is not required now. Another 
method of sieving which is often used but which is not standard, 
is, instead of striking one side against the palm of the hand to 
bounce one side of it gently up and down on a small block of 
wood, taking care that none of the material spills over the top 
of the sieve. The addition of a few shot to the contents of 
the sieve also greatly hastens the operation of sieving, as the 
bouncing of the shot on the wire cloth of the screen keeps the 
meshes of the latter open. To separate the shot from the 
coarse material preparatory to weighing the latter, the mixture 
is passed through a 10- or 20-mesh screen. This method of 
sieving is particularly effective for taking the fineness of raw 
material, hydrated lime, and materials of this character. 

7 . Importance of Fine Grinding. —Generally the finer 
the grinding the more active is the reaction in setting, though 
a fine cement is not necessarily quick-setting. While a very 


—7 


8 


MANUFACTURE OF CEMENT, PART 2 


finely ground cement may not develop as high a neat tensile 
strength as a coarser one, its tensile strength is greater in sand 
tests, and as this is more nearly the test in actual practice, it 
serves as a better indication. The cementing value, or adhesive 
power, of a cement depends on its fineness, and it is claimed 
that the higher results on neat tests with coarse cement is due 
to the fact that the coarser particles act as sand, thereby com¬ 
bining both cohesive and adhesive effects. However this may 
be, it has been conclusively shown by a series of tests on the 
same cement that the samples which were coarsely ground 
gave higher neat tests while those finely ground gave higher 
sand tests. 

8. Limitations of the Sieve Test. —While the sieve 
test is a very good check on the grinding at the mill, too 
great confidence should not be placed in it when examining 
new brands of cement, as a cement ground so that 85 per 
cent, of it will pass a No. 200 sieve may not in reality be so 
fine as one ground only 75 per cent. fine. The cementing 
value of Portland cement depends on the percentage of those 
infinitesimal particles known as flour, and no sieve is fine 
enough to tell the quantity of these particles present. The 
particles retained on the No. 100 and No. 200 sieves have no 
binding power when used with sand and undoubtedly much of 
the cement that passes the No. 200 sieve has very little if any 
binding power. The products of the Griffin mill and of the 
ball and tube mills probably differ much in the percentage of 
flour present, even when testing the same degree of fineness 
on the 200-mesh sieve. Even with the ball- and tube-mill sys¬ 
tem, one ball mill and two tube mills would probably give a 
product with a higher percentage of flour than one tube mill 
and two ball mills even if the cement is ground to the same 
sieve test. The size of the screen on the ball mills probably 
also influences the percentage of flour in a product of a cer¬ 
tain fineness. 

9. Mixing- Cement Pastes and Mortars.— The tests 
that follow are to he applied to either cement pastes or mor¬ 
tars. The term cement paste is used to designate a mixture of 


MANUFACTURE OF CEMENT, PART 2 


9 


cement and water only, while the term mortar applies to mix¬ 
tures of cement, sand, and water. 

In making tests with either pastes or mortars, the quantity 
of dry material to be mixed at one time should not be more 
than 1,000 grams, nor less than 500 grams. If the mixture is 
cement and sand, the two should not weigh more than 1,000 
grams. The temperature of the room and the mixing water 
should be as nearly 70° F. as possible. 

The dry materials are first weighed and placed on a large 
plate of thick glass, a slab of slate or stone, or a sheet of brass 
about 2 feet square and a crater formed in the center. The 
proper percentage of clean water is then 
poured into the crater and the material 
on the outer edge is turned into the 
crater by means of a trowel. As soon 
as the water has been absorbed, which 
should not require more than \ minute, 
the operation is completed by kneading 
the cement with the hands vigorously for 
an additional 1 to 3 minutes, the process 
being similar to that used in kneading 
dough. A sand-glass affords a convenient 
guide for the time of kneading. During 
the operation of mixing the hands should 
be protected preferably by rubber gloves. 

10 . Normal Consistency.—In or¬ 
der to determine the setting time, strength, 
etc., of cement, it is necessary to establish 
a standard of consistency, as the percentage of water added to 
a sample of cement influences its setting time. This standard 
of consistency is termed the normal consistency of cement and 
under standard rules is determined by means of the Vicat 
apparatus shown in Fig. 2. This device consists of a frame a 
that bears a movable rod b weighing 300 grams, one end c 
being 1 centimeter in diameter for a distance of 6 centimeters 
and the other having a removable needle d, 1 millimeter in 
diameter and 6 centimeters long. The rod is reversible, moves 






















10 


MANUFACTURE OF CEMENT, PART 2 


freely up and down, and can be held in any desired position 
by the screw e. To the rod b is attached an indicator f that 
moves over a scale s (graduated to millimeters) attached to 
the frame. The mortar is held by a conical hard-rubber ring c 
which rests on a glass plate h. The ring c is 7 centimeters in 
diameter at the base and 4 centimeters high. 

In making the determination of consistency the same quantity 
of cement as will subsequently be used for each batch in mak¬ 
ing the briquettes (but not more than 1,000 nor less than 500 
grams) is kneaded into a paste, as already described, and 
quickly formed into a ball with the hands, the operation being 
completed by tossing the ball six times from one hand to the 
other, the hands being held 6 inches apart. The ball resting 
in the palm of one hand is then pressed into the larger opening 
of the conical rubber ring g held in the other hand, completely 
filling the ring with the paste. The excess at the larger end is 
then removed by a single movement of the palm of the hand 
and the ring placed with the larger end downward on the glass 
plate. The mortar rests on this glass plate and the upper, or 
smaller, surface is smoothed oflf with a trowel held at a slight 
angle with the top of the ring. During the filling of the ring 
care must be taken not to compress the paste. 

The rod is now so adjusted that the lower end of the cylinder 
is in contact with the surface of the cement mixture. The 
indicator is read, the rod is quickly released by a turn of screw 
and the cylinder, owing to its weight, penetrates the plastic 
cement mixture. The depth of penetration is read ofif the 
scale. 

The paste is of normal consistency when the cylinder pene¬ 
trates the mass 10 millimeters below its surface witbin -J minute 
after being released. Great care must be taken to fill the ring 
exactly to the top. The trial pastes are made with varying 
percentages of water until the correct, or normal, consistency 
is obtained. 

11 . Setting Time. —The term set is used to define the 
change undergone by tbe cement passing from the plastic to 
the solid state and has no bearing at all on the hardening of 


MANUFACTURE OF CEMENT, PART 2 


11 


the cement. It is usually divided into two arbitrary periods 
called the initial set and the final set. 

' i 

12 . Method of Determining Setting Time.— To test 
the set, a paste of normal consistency is molded and placed 
under the rod, Fig. 2. The needle is then carefully brought in 
contact with the surface of the paste and quickly released. 
1 he setting is said to have commenced—that is, the initial 
set takes place—when the needle ceases to pass a point 5 
millimeters above the upper surface of the glass plate within 
i minute and is said to have terminated—that is, the final 
set occurs—the moment the needle does not visibly sink into 
the mass. 

The test pieces, or rings filled with the cement pastes should 
be stored in moist air during the test. This is accomplished 
by placing them on a rack over water contained in a pan and 
covered with a damp cloth, the cloth being kept away from the 
test pieces by means of a wire screen, or they may be stored 
in a moist box or closet. Care should be taken to keep the 
needle clean, as the collection of cement on the sides of the 
needle interferes with its penetration, while cement on the point 
of the needle tends to increase its penetration. 

The determination of the time of setting is only approximate, 
being materially affected by the temperature of the mixing 
water, the temperature and humidity of the air during the test, 
the percentage of water used, and the amount of kneading and 
molding the paste receives. 

13 . Gilmore’s Needles. —The test proposed by General 
Gilmore, U. S. A., for determining setting properties is the 
one most frequently used in the United States. It consists in 
mixing neat cement to a stiff plastic consistency, making cakes 
2 or 3 inches in diameter and J inch thick from this mixture, 
and observing how much time elapses before they will bear a 
needle 1/12 inch in diameter and weighted with \ pound. When 
the cake is firm enough to bear the needle the time is noted as 
the beginning of the set, or in other words, the time of initial 
set. The cakes, or pats, should be made with a flat top, so 
as not to catch the edge of the needle. Trials are next made 


12 


MANUFACTURE OF CEMENT, PART 2 


every now and then with a 1/24-inch needle weighted with 1 
pound. The time at which the cake is firm enough to bear 
the needle, is noted as the end of the set. The Gilmore needles, 
or wires, illustrated by Fig. 3, are much more convenient to 
use when many samples have to be tested, as the pats them¬ 
selves do not have to be lifted from the moist closet or table 
in order to apply the needle. While the Vicat needle unques¬ 
tionably is a more scientific instrument and should be used in 
all cases where great precision is required in making tests, as 
in settling disputes, etc., still, for ordinary inspection work 
where all that is needed is the assurance that the cement will 

not set before it is laid in 
position, and that after it is 
so placed it will harden in a 
reasonable time, the simpler 
and less expensive Gilmore 
needles will answer the pur¬ 
pose just as well as the more 
expensive Vicat apparatus. 
Gilmore’s needles are the 
ones generally used both by 
manufacturers and by engi¬ 
neers in determining the set¬ 
ting time of cement and most men called on to test and use 
cement are familiar with the terms initial and final set as used in 
connection with these needles. 

14. Ball Test for Normal Consistency. —The ball 
test for determining the proper consistency is employed to a 
great extent in commercial laboratories where the Gilmore 
needles are used to determine the set. In spite of its crude¬ 
ness the ball test gives results that agree fairly well with 
those determined by the Vicat apparatus. The hall test con¬ 
sists in forming the mortar into a ball and dropping it from 
a height of 1 foot. This fall should not materially flatten 
nor crack the ball; flattening would denote too much water 
in the mortar and cracking would indicate that there was not 
enough. 



Fig. 3 


















MANUFACTURE OF CEMENT, PART 


O 


13 


15. Moist Closet. —A convenient form of moist closet 
for use when only eight or twelve pats are to be tested at a 
time is shown in Fig. 4. It is made from an ordinary tin bread 
box, such as can be procured of any dealer in tinware. A 
removable shelf made of -J-inch-mesh wire netting is held about 
midway between the top and bottom of the box by means of 
cleats and is stiffened by means of strips of folded tin. A wet 
sponge is placed in the bottom of the box and the pats are 
placed on the shelf. The box is to be kept closed, of course, 
except when applying the needles to the pats. Where many 
pats are tested a moist closet may be made by lining a wooden 
cupboard or clothes 
press of suitable 
size with tin. The 
shelves therein 
should slide in and 
out and a pan of 
water containing a 
large sponge should 
be placed in the 
closet 


16. Influence 
of Temperature, 

Etc., on Setting- 
Time. — The rate 
of set is influenced by a number of things chief of which 
are temperature and the percentage of water used in making 
the mortar. The higher the temperature the quicker the 
set, the larger the percentage of water the slower the set. 
Temperature has a very marked influence on the setting time, 
and many cements that are suitable for use in the United 
States could not be used in the tropics. Similarly in the early 
spring and late fall, when the temperature out of doors is from 
20 to 30° F. below what it is indoors, cement that sets rather 
quickly in the laboratory may give perfect satisfaction when 
used outside. The percentage of water used to gauge the pats 
or, in actual work, to make the mortar, very greatly affects the 



Fig. 4 



























































14 


MANUFACTURE OF CEMENT, PART 2 


setting time as well as the early strength of the concrete. A 
wet mixture sets very slowly while a dry one sets much more 
promptly. 

17. Addition of Retarders to Cement. —If Portland- 
cement clinker is ground just as it comes from the coolers 
without the addition of any foreign substance, the resulting 
cement is entirely too quick-setting to allow it to be worked 
properly. It is, therefore, the general practice either to grind 
a small percentage, usually 2 or 3 per cent., of gypsum with the 
clinker or to add to the cement just before it is shipped a 
corresponding percentage of finely ground plaster of Paris, 
in order to regulate the set so as to give time for working, 
tamping, and troweling. At some mills coarsely ground plaster 
of Paris, or calcined plaster, as the manufacturers call it, is 
added to the clinker before grinding. 

Le Chatelier made many experiments on the effect of the 
addition of gypsum and plaster of Paris to Portland cement. 
He concluded that the governing action it exe r cised over the 
cement was due to the formation of certain soluble compounds 
between the sulphuric acid of the calcium sulphate and the 
very active calcium aluminates of the cement that cause quick¬ 
setting. He also stated that either gypsum or plaster of Paris 
could be added to retard the set. 

Calcium chloride will retard the setting of cement although 
it had never been used for that purpose in mill practice. Candlot 
made many experiments to determine the effect of calcium 
chloride on the setting time of ground-cement clinker and found 
that from J to 1 per cent, of calcium chloride was needed to 
produce the maximum effect. Beyond a certain point, how¬ 
ever, addition of both plaster of Paris and calcium chloride 
make cement quick-setting again. Thus cement without any 
retarder set in 6 minutes; with 2 per cent, plaster of Paris 
added, it set in 6 hours, and with 5 per cent, plaster it set in 
1 hour and 30 minutes. Gypsum, however, can be added to 
cement in any proportion without quickening its set. 

Some cement is so quick-setting that it even sets under the 
trowel and on working gets dryer instead of more plastic. When 


MANUFACTURE OF CEMENT, PART 2 


15 


cement sets within a few minutes after water is mixed with it, 
it is said to have a flash set . 

18. Effect of Aeration on Setting 1 Time. —Slow-set¬ 
ting Portland cement may become quick-setting on storage and 
quick-setting cement may season into slow-setting cement. 
Quick-setting cements, or cements that become quick-setting, 
are usually high in alumina and low in lime; consequently to 
remedy this defect it is necessary to increase the lime or to 
cut down the amount of alumina. Cement that is very much 
underburned is likely to be quick-setting but underburning is 
rarely ever the cause of quick-setting. Rapid cooling of the 
clinker helps to make cement slow-setting. 

Where cement has become quick-setting from storage, it can 
generally be made slow-setting again either by adding from 1 
to 2 per cent, of slaked or hydrated lime to it or by mixing 
the mortar with lime water. When cement becomes quick¬ 
setting from age, or long storage, it is customary to bring the 
setting time back to normal by adding plaster of Paris. Usu¬ 
ally a certain quantity of plaster of Paris, as measured by 
means of a square box made to hold just so much when struck 
off level, is added to every barrow of cement as it is wheeled 
from the bin to the conveyer; or else a boxful of plaster of 
Paris is dumped into the conveyer at stated intervals of time. 
The screw conveyer then does the mixing. Quick-setting 
cements may also be made slow-setting by mixing them with 
slow-setting ones, but this must be done carefully to see that 
cement of both kinds is supplied in the desired propor¬ 
tions. 


19. Tensile Strength. —The tensile strength of cement 
is determined by using test pieces of cement mixed with sand 
molded in the form of briquettes. The smallest cross-section 
of these briquettes is 1 square inch in area. They are allowed 
to harden in air for 24 hours and are then kept in water and 
broken at stated intervals. Tensile tests of neat cement were 
at one time required and while not now specified are made as a 
matter of scientific record. 


16 


MANUFACTURE OF CEMENT, PART 2 


20 . Standard Sand for Briquettes. —The sand used 
to test the mortar strength of cement is the natural sand from 
Ottawa, Illinois. This sand is screened to pass a sieve having 
20 meshes per linear inch and retained on a sieve having 30 
meshes per linear inch, the wires to have diameters of .0165 and 
.011 inch, respectively; that is, half the width of the opening in 




each case. Sand having passed the 20-mesh sieve is considered 
as standard when not more than 1 per cent, passes a 30-mesh 
sieve after 1 minute of continuous sifting of a 500-gram sample. 
This sand may be obtained from the Ottawa Silica Company, 
Ottawa, Illinois. 

21. Form of Briquette. —The form of the present stand¬ 
ard briquette is shown in Fig. 5. It differs from the old standard 



Fig. 7 



form only in that the corners are rounded. For forming these 
briquettes, a single mold, Fig. 6, and a gang mold, Fig. 7, are 
used. The former gives slightly higher results, but the latter 
is more convenient because it permits a number of briquettes 
to be made at one time. The molds should be made of non- 
corrosive metal such as brass, bronze, or gun metal. After 




























































































































MANUFACTURE OF CEMENT, PART 2 


17 

being used the molds should be freed from caked cement by 
brushing them with a stiff scrubbing brush and scraping them 
with a piece of soft metal such as copper or zinc. After clean¬ 
ing they should be wiped with an oily cloth and kept in a place 
free from dust. 


22. Molding the Briquettes. —The first step in making 
the briquettes is to find out the quantity of water necessary to 
make a paste of normal consistency by the method previously 
outlined. This is the quantity of water to be used for neat 
briquettes. The proper quantity of water for sand mortar is 
then ascertained by referring to Table I. Next, the proper 

TABLE I 

PERCENTAGE OF AVATER FOR STANDARD MORTARS 


Percentage of 
Water for Neat 
Cement Paste 
of Normal 
Consistency 

Percentage of 
Water for One 
Cement Three 
Standard Ottawa 
Sand* 

Percentage of 
Water for Neat 
Cement Paste 
of Normal 
Consistency 

Percentage of 
Water for One 
Cement Three 
Standard Ottawa 
Sand* 

15 

9.0 

23 

10.3 

16 

9.2 

24 

10.5 

17 

9.3 

25 

10.7 

18 

9.5 

26 

10.8 

19 

9.7 

27 

11.0 

20 

9.8 

28 

11.2 

21 

10.0 

29 

11.3 

22 

10.2 

30 

11.5 


*Note. —The quantity of water is expressed in percentage of the com¬ 
bined weight of cement and sand. Thus, if 22 per cent, water is required 
for normal consistency, 102 cubic centimeters of water will be needed 
for a mixture of 250 grams of cement and 750 grams of sand. 

quantities of cement and sand are weighed. For mortar 
briquettes the proportions are one of cement to three of sand 
and the combined weight of the two must lie between the limits 
of 500 and 1,000 grams. Usually 250 grams of cement and 
750 grams of sand are employed. This weight will make 















18 


MANUFACTURE OF CEMENT, PART 2 


seven or with care eight briquettes. The two materials are then 
carefully mixed dry, the water added and the mixing done as 
already directed. 

Having worked the paste or mortar to the proper consistency, 
it is at once placed in the molds, pressed in firmly with the 
thumbs and smoothed off with a trowel without ramming. The 
material should be heaped up on the upper surface of the mold, 
and in smoothing off, the trowel should be drawn over the mold 
in such a manner as to exert a moderate pressure on the excess 
material. The mold should be turned over and the operation 
repeated. Instead of kneading the cement mortar with the 
hands, as prescribed by the standard rules, most testers use a 
trowel, working the mortar back and forth on the table under 
the trowel until the desired plasticity is secured. 

23. Breaking the Briquettes. —The briquettes are 
usually left in the molds over night, the molds and contents 
being placed in the moist closet or else covered with damp cloth. 
In the morning they are usually removed from the molds and 
kept in a moist closet for the balance of the 24 hours, after 
which they are placed in tanks and broken at intervals. The 
periods of breakage vary, but are usually 7 days, 28 days, 3 
months, 6 months, 1 year, 2 years, and 5 years after making. 
When neat briquettes are made these are usually broken at the 
24-hour period also, and these have, of course, never been placed 
in water. Nearly all cement testers make and break the 7-day 
and 28-day briquettes as required by the standard specifications, 
but some make no longer-period tests. The average tensile 
strength shown by at least three breaks or the strength of all 
the briquettes broken at each period is taken as the strength 
for that period. It should be noted, however, that where bri¬ 
quettes are manifestly faulty or give strengths differing by 
more than 15 per cent, from the average value of all briquettes 
from the same sample and broken at the same period, the result 
of the tests of these briquettes should not be included in the 
average. Sometimes five briquettes are broken for each period, 
this larger number giving a better average value for the tensile 
strength of the cement 


MANUFACTURE OF CEMENT, PART 2 


19 


24. Briquette Tanks. —Where much testing has to be 
done a good form of trough for the storage of briquettes is 
made of stout 2-inch boards covered with sheet zinc. These 
troughs may be placed one above the other on a suitable wooden 
frame. A small stream of water should be kept running through 
them all the time. This can be done by arranging overflow 
tubes so that the water will flow from the upper trough into 
the next one below, etc. After the briquettes have attained 
their initial set and before being removed from the molds they 
should be marked with an identifying number and date by 
means of a marking brush and black paint or a black (carbon) 
grease pencil or crayon. Blue or other aniline pencil should 
not be used, as the alkali in the cement will discharge the color 
in time and render the marking invisible. Neat briquettes may 
also be marked by means of a steel die, when the marking 
should be done in the corners and never across the breaking 
section. Sand briquettes may also be marked by putting on a 
thin layer of neat cement, about 1/16 inch thick and marking 
this with a die. Where both neat and sand briquettes are 
made, frequently only the neat briquettes are marked and when 
these are placed in the tanks the neat briquettes are placed on 
top of the corresponding sand ones so as to make identification 
of the latter possible. 

In storing the briquettes in the troughs it will be found most 
:onvenient to put all the briquettes to be broken in 7 days in 
order of breaking, in one part of the trough and those for 28 
days in another. The briquettes may be placed edgewise in 
pairs, one on top of the other. 

25. Briquette Testing' Machines. —The best-known 
form of machine for breaking the briquettes is the Fairbanks 
automatic cement-testing machine, which is shown in Fig. 8. 
It consists of a cast-iron frame a made in one piece with a shot 
hopper b. To this frame are hung the two levers c and d. 
From the end of the upper lever d the weight is applied by 
allowing shot to flow from the hopper into the bucket /. The 
tension is applied to the briquettes held in the clips h by means 
of the lower lever c. The lower clip is attached by means of 


20 


MANUFACTURE OF CEMENT, PART 2 


a ball point to a screw with hand wheel p for lowering or 
raising it when putting in the briquettes and taking up the slack. 
There is also a counterbalance e for bringing the levers and 
bucket into partial equilibrium so that the final adjustment can 
be made with the ball l. The shot hopper is provided with a 



Fig. 8 

lever t and gate j that cuts off the shot as soon as the 
specimen breaks. By hanging the bucket on the opposite 
end of the lever d the shot is weighed by means of a sliding 
poise r. 

To operate the machine hang the bucket f on the end of the 
beam d as shown. See that the poise r is at the zero mark and 
















































































































































MANUFACTURE OF CEMENT, PART 2 


21 


balance the beam by turning the ball l. Fill the hopper b with 
fine shot, place the specimen in the clamps h, and adjust the 
hand wheel p so that the graduated beam d will rise midway to 
the stop k. Open the automatic valve j to allow the shot to run 
slowly into cup /. As the shot drops into the bucket the 
graduated beam d will fall; tension should therefore be applied 
by turning the crank m to keep the beam d in mid-position. 
The shot is then allowed to run until the specimen breaks. 
When the specimen breaks the graduated beam d will drop and 
automatically close the valve j. 

Remove the bucket with the shot in it and hang the counter¬ 
poise weight g in the place where the bucket was. Hang the 
bucket f on the hook under the large ball e and proceed to 
weigh the shot in the regular way, using the poise r on the 
graduated beam d and the weights n on the counterpoise weight 
g. The result will show the number of pounds required to 
break the specimen. The flow of shot, which can be regulated 
by the cut-off valve j, should be such that the quantity run into 
the bucket in 1 minute when balanced against the weights, is 
equivalent to 600 pounds. The briquettes should be broken as 
soon as removed from the water. 

26. Soundness, or Constancy of Volume. —The 

soundness of cement is determined by making pat tests. Cement 
is mixed as for neat briquettes except that, generally, from 10 
to 15 per cent, more water is used. After being thoroughly 
worked the mixture is placed on a glass plate about 4 inches 
square and made into a cake, or pat, that is about 3 inches in 
diameter, inch thick at the center, and drawn out to a thin 
edge at the circumference. In molding the pat, the cement is 
first flattened on the glass and the pat then formed by drawing 
the trowel from the outer edge toward the center. About 100 
grams of cement is sufficient for a pat. As soon as made the 
pat is placed in a moist closet and allowed to remain there for 
24 hours. It is then placed on a shelf in a loosely covered 
vessel of boiling water and steamed for 5 hours. The pats 
should be well above the water and the latter should be vigor¬ 
ously boiled. To pass the test the pats should be firm and hard 


22 


MANUFACTURE OF CEMENT, PART 2 


after the steaming or boiling and when small pieces of the 
edges are broken off between the thumb and forefinger they 
should break with a snap and not merely crumble between the 
fingers. The pat also should not show wedge-shaped radial 
cracks from the center. No attention need be paid to the pat 
coming off the glass, nor should a slight curvature, amounting 
to, say i inch, provided the pat is sound and hard, be considered 




Fig. 9 


Fig. 10 


an indication of serious unsoundness. The heat alone may 
cause the glass to be cracked and broken, but since the coeffi¬ 
cients of expansion of cement and glass are not the same some¬ 
thing must give way, if the cement sticks to the glass; conse¬ 
quently as the glass is the weaker, it is usually the one to crack. 
The pats should remain on the glass, but their coming off is not 
an indication of unsoundness, provided they do not show ex¬ 
treme curvature or distortion. 

Curvature can best be ascertained by placing a ruler across 
the bottom of the pat. Sometimes pats are made up too wet, 

in which case they are liable 
to crack on drying. These 
cracks can be readily distin¬ 
guished from those due to 
unsoundness, as the latter 
always radiate from the 
center and are wedge-shaped, with the point of the wedge at the 
center, while the cracks due to drying are not wedge-shaped and 
do not radiate from the center. Fig. 9 shows a pat with drying 
cracks, and Fig. 10, one with the radial wedge-shaped cracks 
due to unsoundness. Fig. 11 shows a distorted pat and the 
method of detecting curvature. 









MANUFACTURE OF CEMENT, PART 2 


23 


27 . Cau es of Unsoundness.— Unsoundness is usually 
due to the presence of free lime in the cement. The presence 
of free lime may be due to several sources. The cement may 
be poorly proportioned and too much lime may be present to 
satisfy the acid elements silica and alumina, or the raw materials 
may be so coarsely ground that these elements cannot come 
into sufficiently close contact with each other to unite properly; 
finally, the temperature of burning may not have been high 
enough to bring about the combination. Often, too, cement 
that is unsound because it is coarsely ground would become 
sound with finer grinding. 

Hydrated or slaked lime may he mixed with cement in all 
proportions and will not cause unsoundness. Calcium carbonate 
is also without effect on it and quicklime ground extremely 
fine also has no injurious action when mixed with cement, be¬ 
cause when water is added to the mixture the lime promptly 
slakes. The free lime that does the damage, therefore, is that 
portion of it which is locked up in a kernel of clinker. The 
clinker forms a protecting casing over the free lime, and when 
the cement is made into mortar the water cannot get at the free 
lime to slake it until after the cement sets. In time, however, 
after the cement has hardened, the water breaks through the 
case of clinker and hydrates the free lime. Now, when lime 
slakes, expansion takes place; consequently, the particles of 
free lime swell with great force and crack the fully hardened 
concrete, just as water in freezing in an iron pipe will burst 
the pipe. By fine grinding, the coarse kernels of clinker in the 
cement are broken up, and water used in mixing the mortar 
can get at the lime to slake it before the cement sets. 

28 . Curing of Unsound Cement. —Unsound cement 
can usually be made sound by seasoning or storing it, when the 
moisture of the air will slake the free lime that is present. 
Unsound cement can also sometimes be made sound by the 
addition of from J to 1 per cent, plaster of Paris. It is a com¬ 
mon error to suppose that an excess of plaster of Paris causes 
cement to expand and crack. Either plaster of Paris or gypsum 
may be added to cement in large proportions without causing 


386—8 


24 


MANUFACTURE OF CEMENT, PART 2 


unsoundness. Magnesia is also supposed to cause expansion; 
cement may, however, contain 5 per cent, of this element with¬ 
out showing any ill effects from it. 


CORRECTING FAULTY PORTLAND CEMENT 

29. When cement fails to pass the required physical tests, 
the following remedies may be applied : 

Unsoundness 

1. Lower the percentage of lime in the raw material. 

2. Burn the clinker harder. 

3. Grind the raw materials finer. 

4. Season the cement or clinker. 

5. Add a little more gypsum or plaster of Paris. 

6. Grind the cement itself finer. 

Quick Setting 

1. Raise the percentage of lime in the raw material. 

2. Increase the amount of gypsum or plaster of Paris. 

3. When it is possible to do so, replace some of the alumina 
of the mixture by ferric oxide or silica; that is, use a more 
silicious or ferruginous clay. 

4. If unsound also, burn the clinker harder and season the 
cement. 

5. Cool the clinker quickly with water. 

Low 7-Day Tensile Strength 

1. Increase the percentage of lime. 

2. Increase the amount of alumina and decrease the amount 
of silica. 

3. Increase the amount of gypsum slightly. 

Too High 7-Day Tensile Strength 

If unsound, apply remedies given under Unsoundness 

1. Decrease the percentage of lime. 

2. Burn the clinker harder. 

3. Grind the clinker coarser. 

4. Add less gypsum or plaster. 



MANUFACTURE OF CEMENT, PART 2 25 

5. Increase the amount of silica and decrease the amount of 
alumina. 

6. Replace some of the alumina by iron oxide. 

7. Season the cement. 

Low Sand Strength 

1. Grind the clinker finer. 

2. Increase neat strength, if low, by methods outlined under 
Low 7-Day Tensile Strength. 

Low Specific Gravity 

1. Burn the clinker harder. 

2. Do not store too long. 


CHEMICAL ANALYSIS OF PORTLAND CEMENT 

AND RAW MATERIALS* 


ANALYSIS OF PORTLAND CEMENT 

30. The principles involved in the quantitative analysis of 
cement differ in no way from those laid down for other mineral 
analyses, but specialization being necessary in all lines of work 
it is natural that cement chemists should evolve methods pecu¬ 
liarly adapted to the material in hand. In cement laboratories 
it is necessary to arrive at fairly accurate results in a short 
space of time, and any method of yielding results accurate to 
.2 per cent, will serve the purpose, as two samples drawn from 
the same barrel and analyzed by the standard and more accurate 
methods will be found to vary that much. 

Portland cement will be found to dissolve more or less com¬ 
pletely on digestion with dilute hydrochloric acid, the complete¬ 
ness with which the cement dissolves depending on the care 
with which it has been made and the strength of the acid used 
to decompose it. A good, well-burned Portland cement will 
usually dissolve in dilute (1:3) hydrochloric acid without leav¬ 
ing a residue of more than .2 per cent. The scheme outlined 

*In connection with this Section, the student is referred to Quantitative 
Analysis y taking especial note of the precautions there given. 





26 


MANUFACTURE OF CEMENT, PART 2 


here has been gradually worked out in the laboratory and yields 
satisfactory results. Before submitting the cement to a chem¬ 
ical analysis, it should be passed through a 100-mesh test sieve 
to free it from pieces of clinker too large to be attacked quickly 
by the acid. 

31. Determination of Silica. —Weigh .5 gram of cement 
into a wide platinum or porcelain dish. The former is the 
more expensive of the two, but it is a better conductor of heat, 
and there is no danger of the solution becoming contaminated 
with silica, etc. from the dish. Now stir up the sample of 
cement in the dish with 10 cubic centimeters of cold water 
until all lumps are broken, and add immediately 10 cubic centi¬ 
meters of cold dilute (1:1) hydrochloric acid. Place the dish 
on a water bath and evaporate to dryness, stirring occasionally. 
The water bath will evaporate as fast as anything else and there 
is no danger of the silica spattering, which it is liable to do 
when a hot plate is used, unless the operation is very carefully 
watched. As soon as the contents of the dish is dry place it in 
an air bath and drv at 100° to 110° C. for 1 hour. Cool, add 
10 cubic centimeters of dilute hydrochloric acid and 20 cubic 
centimeters of water to the contents of the dish, cover with a 
watch glass and digest on the hot plate for 5 or 10 minutes. 
Filter off the silica on a 9-centimeter filter, wash from seven 
to ten times with hot water, put in a weighed platinum crucible, 
ignite over the Bunsen burner until all the filter paper is con¬ 
sumed, and then ignite strongly over a blast lamp for 10 minutes. 
Cool in a desiccator and weigh as Si0 2 ; multiply the weight 
by 200 for percentage of silica, Si0 2 . 

32. Determination of Iron and Alumina. —Heat the 
filtrate to boiling and add a small but distinct excess of am¬ 
monia. This can be most conveniently done by means of a bottle 
fitted with a siphon tube the end of which terminates in a jet 
connected to it by a short piece of rubber tubing, which is 
closed by a pinch cock, as shown in Fig. 12. The bottle stands 
on a shelf over the reagent table and the siphon extends to 
within 6 inches of the surface of the table. The beaker is 
placed under the jet and the ammonia can be added very care- 


MANUFACTURE OF CEMENT, PART 2 


27 


fully and conveniently by pressing the pinch cock. After adding 
the ammonia, replace the beaker on the hot plate and boil for 
5 minutes. Remove from the hot plate and allow the precipi¬ 
tate to settle. Filter on an 11- 
centimeter filter paper and wash 
once with hot water to collect the 
precipitate in the cone of the filter. 

Invert the funnel over the beaker 
in which the precipitation was made 
and wash practically all of the 
precipitate back into the beaker, 
allowing the filter paper to remain 
in the funnel. Dissolve the precipi¬ 
tate in 20 cubic centimeters of 1:5 
nitric acid and dilute the solution to 
100 cubic centimeters. Heat to 
boiling and reprecipitate with am¬ 
monia as before. Boil for 5 min¬ 
utes, allow the precipitate to settle, 
and filter through the same filter 
paper as used for the first precipi¬ 
tate. Wash once with hot water, 
ignite carefully in a weighed cru¬ 
cible over a Bunsen burner, and 
finally with the blast lamp for 5 
minutes. Cool and weigh as com¬ 
bined oxides of iron and aluminum 
Fe 2 0 z J rAl 2 0. i . This precipitate 
also contains phosphoric, P 2 0 5 , 
and titanic, Ti0 2 , acids, both of 
which are present in small quan¬ 
tities in cement, Fig - 12 



33. Determination of Lime. —Make the filtrate from 
the iron and alumina alkaline with ammonia; boil, and add 
20 cubic centimeters of boiling saturated ammonium-oxalate 
solution, or, better, 2 grams of solid ammonium-oxalate dis¬ 
solved in from 25 to 50 cubic centimeters of boiling water 

























































































28 


MANUFACTURE OF CEMENT, PART 2 


just prior to use. This may be measured instead of weighed 
with a small marked test tube. Stir well, allow 15 minutes 
to settle, filter on an 11-centimeter filter and wash ten times 
with hot water, using as little as possible, about 100 to 125 
cubic centimeters to do the work well. -Transfer the paper 
and precipitate to the beaker in which the latter was formed, 
and open the paper and spread it out against the upper side 
of the beaker. Wash the precipitate ofif the paper with a jet 
of hot water, hold the paper over and allow it to remain 
against the walls of the beaker; add 50 cubic centimeters of 
dilute (1:4) sulphuric acid, dilute to 150 cubic centimeters, 
and heat until the solution is between 60° and 90° C. Titrate 
with permanganate solution until a pink color is produced. All 
this time the paper should be sticking to the wall of the beaker. 
Now drop the filter paper into the solution and stir. The pink 
color of the latter will he discharged. Finish the titration very 
carefully by adding a drop of permanganate at a time and cal¬ 
culate the lime, CaO, 

34. Determination of Magnesia. —If the filtrate from 
the lime measures over 250 cubic centimeters, acidify and 
evaporate until this bulk is reached. This can be rapidly done 
by using a large, say 8-inch, porcelain dish in the following 
manner: Place a piece of wire gauze on a tripod, and in the 
center place a piece of thin asbestos paper about the size of a 
silver dollar. Now place the dish on this and place a Bunsen 
burner turned fairly low under the dish. The contents of the 
dish can then be made to evaporate rapidly without boiling by 
regulating the flame. When the solution measures 250 cubic 
centimeters transfer to a beaker, cool and when cold add 15 
cubic centimeters of a 10-per-cent, solution of sodium phos¬ 
phate and 15 cubic centimeters of strong ammonia. Stir thor¬ 
oughly and set aside in a cool place for at least 6 hours. Filter, 
wash with a solution made by mixing 800 cubic centimeters of 
water with 300 cubic centimeters of concentrated ammonia 
(specific gravity .96) and 100 grams of ammonium nitrate. 
Place in a weighed platinum or porcelain crucible and ignite 
over a low flame until all the carbon is burned off. (Do not 


MANUFACTURE OF CEMENT, PART 2 


29 


use the blast lamp.) Cool in a desiccator and weigh as mag¬ 
nesium pyrophosphate, Mg 2 P.,0 7 . The weight multiplied by 
.3619 gives the weight of magnesia, MgO ; to get the percentage 
of MgO in the sample, multiply by .7238. 

35. Preparing ancl Standardizing tiie Permanga¬ 
nate.— The most convenient strength for the permanganate 
is 5.64 grams of the salt to a liter of water. One cubic 
centimeter of this solution will then be equivalent to about 1 
per cent, of lime where a .5-gram sample is used. To standard¬ 
ize the permanganate weigh into a 400-cubic-centimeter beaker 
.67 gram of sodium oxalate, which has been especially pre¬ 
pared for use as a volumetric standard. Dissolve in 100 cubic 
centimeters of water and when all is in solution add 10 cubic 
centimeters of dilute (1:1) Ailphuric acid. Heat to 60° C. 
and titrate with the permanganate. The above quantity of 
sodium oxalate is equivalent to .5 gram of calcium car¬ 
bonate or .28 gram of calcium oxide. The value of the per¬ 
manganate solution is found by dividing 28 by the number of 
cubic centimeters of permanganate required by .67 gram of 
sodium oxalate. 

36. Determination of Iron Oxide. —Weigh 1 gram of 
finely ground cement into a small beaker and add 15 cubic 
centimeters of dilute hydrochloric acid, heat from 10 to 15 
minutes and add a little water. Heat to boiling and filter- 
through a small filter, washing the residue well with water and 
catching the filtrate and washings in a porcelain dish. Add to 
the solution 5 cubic centimeters of dilute hydrochloric acid 
and bring to a boil. Add carefully drop by drop stannous- 
chloride solution (35 grams in 100 cubic centimeters of dilute 
1 : 3 hydrochloric acid) until the last drop makes the solution 
colorless. Remove from the burner and cool the liquid by 
setting the beaker in a vessel of cold water. When nearlv 
cold, add 15 cubic centimeters of saturated mercuric-chloride 
solution and stir the liquid in the dish with a glass rod. Allow 
the mixture to stand for a few minutes during which time a 
slight white precipitate should form. Run in standard bichro¬ 
mate solution carefully from a burette until a drop of the iron 


30 


MANUFACTURE OF CEMENT, PART 2 


solution tested with a drop of 1-per-cent, solution of potas¬ 
sium ferricyanide no longer shows a blue color, but, instead, 
a yellow color. Multiply the number of cubic centimeters of 
bichromate used by the ferric-oxide equivalent per cubic centi¬ 
meter of the bichromate and divide the product by the weight 
of the sample. The result, multiplied by 100, gives the per 
'cent, of the ferric oxide, Fc 2 0 3 , in the cement. 

The most convenient strength for the standard bichromate 
.'solution is 3.074 grams of the salt to the liter. One cubic 
'centimeter of this solution is equivalent to .005 gram of ferric 
■oxide. It should be standardized against iron wire or ferrous 
ammonium sulphate. 

37 . Determination of Sulphuric AcicU —Weigh 1 
rgram of the sample into a small dry beaker and stir it up with 
10 cubic centimeters of cold water until all lumps are broken 
up and the lighter particles are in suspension. Add 15 cubic 
centimeters of dilute (1:1) hydrochloric acid and heat until 
the solution is completed. Filter through a small paper and 
wash the residue thoroughly. Dilute the filtrate to 250 cubic 
centimeters, heat to boiling, and add 10 cubic centimeters of 
boiling 10-per-cent, barium-chloride solution. Stir well and 
allow to stand over night. Filter, ignite, and weigh as BaS0 4 , 
which weight multiplied by .34297 gives the weight of SO s . 

38 . Loss of Ignition. —Weigh .5 gram of cement into 
a weighed platinum crucible, cover with a lid, and heat for 5 
minutes over a Bunsen burner, starting with a low flame and 
gradually raising it to its full height. Then heat for 15 
minutes over a blast lamp. Cool and weigh. The loss of 
weight represents the loss on ignition. This loss consists 
mainly of combined water and carbon dioxide driven ofif by the 
heat. Some chemists report, therefore, as carbon dioxide and 
water, or, having found the carbon dioxide, subtract the per¬ 
centage from that of the loss on ignition and call the remainder 
water of combination, or combined water. 

Of the other elements in cement the alkalies are occasion¬ 
ally determined. The method for doing this is similar to 
that used for determining potash and soda in minerals, etc. 


MANUFACTURE OF CEMENT, PART 2 


31 


39. Rapid Determination of Lime (Meade’s 
Method). —It is often useful to know the percentage of lime 
in cement as a check on the composition of the raw material. 
The following method gives quick and very accurate results: 

Weigh .5 gram of cement into a dry 500-cubic-centimeter 
beaker and add with constant stirring 20 cubic centimeters of 
cold water. Break up the lumps and when all the sample ex¬ 
cept the heavier particles is in suspension, add 20 cubic centi¬ 
meters of dilute (1:1) hydrochloric acid and heat until the 
solution is completed. This usually takes 5 or 6 minutes. Heat 
to boiling and add carefully to the solution dilute ammonia (96 
specific gravity) until a slight permanent precipitate forms. 
Heat to boiling and add 10 cubic centimeters of a solution of 
oxalic acid (100, grams to the liter). Stir until the oxides of iron 
and aluminium are entirely dissolved and only a slight precipitate 
of calcium oxalate remains. Add 200 cubic centimeters of boil¬ 
ing water and sufficient saturated solution of ammonium oxalate, 
say 20 cubic centimeters, to precipitate the lime. Boil and stir 
for a few moments, remove from the heat, allow the precipitate 
to settle, and filter on an 11-centimeter filter. Wash the pre¬ 
cipitate and paper ten times with hot water, using not more 
than 10 to 15 cubic centimeters of water each time. Remove 
the filter from the funnel, open and lay against the sides of 
the beaker in which the precipitation was made, wash from 
the paper into the beaker with hot water, add dilute sulphuric 
acid, fold the paper over, and allow to remain against the 
walls of the beaker. Heat to 80° C. and titrate with stand¬ 
ard permanganate until a pink color is obtained; now drop in 
the filter paper, stir until the color is discharged and finish the 
titration carefully drop by drop. 

40. Insoluble Residue. —Weigh 1 gram of cement into 
a beaker and stir up with 10 cubic centimeters of water. Add 
5 cubic centimeters of concentrated hydrochloric acid, and 
warm until effervescence ceases. Dilute the liquid to 50 cubic 
centimeters and heat until all soluble matter is in solution and 
only white flakes remain. Filter on a 9-centimeter filter, wash 
with cold water then drop the filter paper into the beaker in 


386—9 


32 


MANUFACTURE OF CEMENT, PART 2 


which solution was effected. Pour 30 cubic centimeters of a 
5-per-cent, sodium carbonate solution into the latter, and digest 
the filter with the sodium carbonate solution for 15 minutes 
at a temperature just short of boiling. Filter the residue and 
old filter on a new filter, wash with cold water several times, 
then with hot hydrochloric acid (1:9) and finally with hot 
water. Ignite at a red heat and weigh as insoluble residue. 


ANALYZING AND PROSPECTING THE RAAV MATERIALS 

41. Before locating a mill at any point, it is important 
to determine accurately the quantity and quality of the raw 
materials that it is desired to use. 

42. Limestone and Cement Rock. —In prospecting 
deposits of limestone and cement rock they should be sampled 
by means of a core or churn drill, and the test holes should be 
sunk to a considerable depth. Surface samples knocked off 
here and there are of little value, and the time spent in analyzing 
any number of them is in most cases thrown away. In sampling 
limestone or other solid material the surface dirt and clay should 
be shoveled away and the weathered rock removed. The drill 
can then be set up and the sample taken. In prospecting a 
limestone property it is customary to make a map showing the 
topography, etc., and this should be divided into squares having 
sides of, say, 25, 50, or 100 feet. Drill holes can then be sunk 
at the corners of each square, and the cores or chips brought 
up by the drill can be saved for analysis. Usually it is the 
custom instead of making one sample of all the rock brought 
up by the drill from a hole, to make separate samples of the 
material brought up from various depths. Thus, one sample 
would represent the material brought up from a hole from 
5 to 10 feet deep, while the next would represent that taken 
by the drill in going from 10 to 15 feet, etc. In this manner, 
the uniformity of the deposit as well as its freedom from 
bands of magnesian stone, etc., can be tested. 

43. Clay.— Clay may be sampled in a number of ways, 
such as by digging pits or by sinking test holes by means 



MANUFACTURE OF CEMENT, PART 2 


33 


of an auger drill or a serrated pipe; that is, a pipe filed on 
the lower end so as to form sharp teeth like those of a saw. 
Hard clays and shales will require either the auger or the 
churn drill. The serrated pipe is forced down into the clay 
by twisting a handle at the upper end. The result when with¬ 
drawn is a plug of clay which fills the pipe and represents the 
strata through which the pipe has passed. 

44. Marl.— For sampling marl, a tube similar to that used 
in sampling cement or the serrated pipe already described may 
be used. If the marl deposit is very wet, a long pipe having a 
plug at one end will be found serviceable. This plug should 
be of iron and have a sharp point. It should fit the mouth of 
the pipe closely and be fastened to a long, thin, iron rod. In 
using the sampler the iron plug is drawn up against the mouth 
of the pipe and the pipe is shoved down to the depth at which 
the sample is to be taken. The pipe is then raised and shoved 
down to its former level, being forced tight against the iron 
plug. The pipe is then raised by means of the rod and the 
sample dumped out. Marl deposits should be carefully mapped 
out in order that the quantity available may be calculated, as 
this is often an important consideration. 

45. Calculating' the Amount of Material Avail¬ 
able. —Before locating a cement plant at any point, the promoters 
should make sure that the deposit is extensive enough to furnish 
the raw material for many years. The first step is to map out 
the supply, and, if possible, determine its depth. The number 
of tons present can then be calculated from the data given in 
Table II. 

Since, on an average 610 pounds of mixed raw material will 
be required to produce one barrel of cement, the calculation of 
the amount of cement that can be made from the deposit as 
mapped out is then simple, and can best be explained by an 
example: Let it be supposed that the area of a prospected marl 
deposit is 1,987,600 square feet, and that its average depth is 31 
feet. The average composition of the marl is 95 per cent, cal¬ 
cium carbonate and of the clay to be mixed with it is 5 per cent, 
calcium carbonate. Now, the proportions of clay and marl will 


34 


MANUFACTURE OF CEMENT, PART 2 


TABLE II 

WEIGHT OF VARIOUS RAW MATERIALS FOR PORTLAND 

CEMENT MANUFACTURE 


Raw Material 

Weight in Pounds 
per Cubic Foot 

Weight in Pounds 
per Cubic Yard 

Limestone. 

160 

4,320 

Cement rock. 

156 

4,212 

Marl (wet). 

48 

1,296 

Clay. 

120 

3,240 

Shale. 

160 

4,320 


be 20 : 70. Then, |-§-X610, or about 475 pounds of marl, will 
be required to make a barrel of cement. One cubic foot of marl 
weighs 48 pounds; therefore, the marl deposit will contain 
1,987,600X31X48 = 2,957,548,800 pounds, and since 475 pounds 
of marl is required to make a barrel of cement, the marl deposit 
is sufficient for 2,957,548,800^475 = 6,226,418 barrels. 

46. Methods of Analysis. —Methods of analysis for 
limestone, clay, and blast-furnace slag have all been given in 
Quantitative Analysis. . The scheme detailed is the best for the 
analysis of cement rock and limestones. The samples should, 
of course, be thoroughly dried at 100° to 110° C. before being 
analyzed, and can best be preserved in small -|-ounce, wide- 
mouth bottles. 

47. Analysis of Cement Rock.— Weigh .5 gram of 
finely ground dried sample into a platinum crucible and mix 
intimately with .5 gram of pure, dry sodium carbonate by stirring 
with a glass rod. Place the crucible over a low flame and 
gradually raise the flame until the crucible is red hot. Continue 
heating for 5 minutes; then substitute a blast lamp for the 
Bunsen burner and heat for 5 minutes longer. Place the crucible 
in a dish or casserole, add 40 cubic centimeters of water and 10 
















MANUFACTURE OF CEMENT, PART 2 


35 


cubic centimeters of hydrochloric acid, and digest until the mass 
is dissolved out of the crucible. Clean off the crucible inside and 
outside add a few drops of nitric acid to the solution and evapo¬ 
rate it to dryness. Heat the residue at 110° C. for 1 hour, cool, 
add 15 cubic centimeters of dilute hydrochloric acid, cover with 
a watch glass, and digest for a few minutes on the hot plate. 
Dilute with 50 cubic centimeters of hot water, heat nearly to 
boiling, and filter. Wash the precipitate with hot water, ignite, 
and weigh as silica. Determine the iron and alumina, lime, mag¬ 
nesia, and loss on ignition as described for cement (see Arts. 
32, 33, 34, 38). To determine sulphur proceed as in deter¬ 
mining this constituent in minerals or iron ores. 


ANALYSIS OP CEMENT MIXTURES, SLURRY, ETC. 

48. Since the success of cement-making depends primarily 
on the proper proportion of calcium carbonate to silica and 
alumina in the mixture, it is highly important to be able to esti¬ 
mate this ratio quickly. If the materials from which the mix¬ 
ture is made are of normal constitution, a determination of the 
calcium carbonate alone will suffice to check the correctness of 
the mixture. For rapidly checking the percentage of calcium 
carbonate, the alkalimetric method, in which the calcium car¬ 
bonate is decomposed by a measured quantity of standard nitric 
or hydrochloric acid, and the excess of acid determined by titra¬ 
tion with standard alkali, is most frequently used in the United 
States. This method does not give very accurate results, how¬ 
ever, and when the exact composition of the mixture is desired, 
resort must be had to the gravimetric methods already outlined. 
When the slurry of the wet process is analyzed, it should first be 
evaporated to dryness, then finely pulverized in a mortar, and 
again dried for half an hour at 110° C. It will then be free 
from moisture and ready for analysis. 

49. Sampling' of Dry Mixtures. —For the control of 
the composition of the mixture of raw materials, it is customary 
to take samples at certain places during the grinding. In the 
dry process, this is usually done either after the material leaves 



36 


MANUFACTURE OF CEMENT, PART 2 


the ball mills, if these are used to do the grinding, or after it 
leaves the Griffin mills, if they are employed for this work. 
When tube mills follow the ball mill it is the custom to check 
the composition of the raw material further after it leaves these 
mills. The sample taken from any of the sources just men¬ 
tioned will need further grinding, but, as a rule, it is not dried 
unless a complete analysis is to be made. Since the rapid scheme 
about to be given is affected by the fineness to which the sample 
is ground, it should be prepared the same way each time by pass¬ 
ing all of it through a 100-mesh test sleeve. 

50. Sampling- of Slurry.— In the wet process the analyt¬ 
ical methods are the same as in the dry process, but the sample 
itself usually has to be freed from a large amount of water 
(from 50 to 60 per cent.) by evaporation and drying. The 
slurry samples are usually taken from the mixing pits, and also 
after the slurry has passed through the tube mills, either from 
the discharge of the mill itself or from the ground-slurry pits. 
In sampling from the mixing pits a common, narrow quart pail 
fastened to the end of a wooden pole by means of a harness snap 
will be found convenient. The pail is put in the slurry bottom 
side up, pushed down to the required depth, and then drawn up. 
As the pole is lifted the pail turns over, fills with slurry, and 
may be lifted out. The vat is usually sampled at three or four 
depths, these samples are mixed, and from the mixture a small 
sample is drawn for testing. The slurry sample is usually 
spread on a sheet of cardboard and dried rapidly on a hot plate, 
after which it is powdered for the analysis. 

51. Checking the Composition of the Mixture.—In 

order to check the composition of the mixture, the following 
solutions should be prepared: (1) Phenol-phthalein indicator; 
(2) f N sodium hydroxide of exact strength; and (3) Hydro¬ 
chloric acid approximately § N. 

One cubic centimeter of the alkali is equivalent to .02 gram 
of calcium carbonate, or 2 per cent, in the mixture if a 1-gram 
sample is used for the titration. After this, prepare a stand¬ 
ard sample of the mixed raw material as this is necessary in 
order to standardize the acid for actual use. By standard 



MANUFACTURE OF CEMENT, PART 2 37 


sample is meant a sample of the mixture whose composition 
has been accurately determined. It should all be ground to 
pass a 100-mesh sieve and dried at 100° to 110° C. After 
drying the sample should be carefully analyzed. This sample 
should contain approximately the quantity of calcium carbonate 
that it is desired to have in the mixture, and the amount of . 
magnesia should also be nor¬ 
mal. When the magnesia 
varies at different times, fresh 
standard samples should be 
prepared to contain these vary¬ 
ing percentages of magnesia; 
otherwise, the lime will be re¬ 
ported too high or too low. 

52. Method of Stand¬ 
ardizing the Acid.— Weigh 
1 gram of the standard sample 
into a 600-cubic-centimeter 
Erlenmeyer flask and run in 
from a pipette 50 cubic centi¬ 
meters of standard acid. Close 
the flask with a rubber stopper 
having inserted through it a 
glass tube about 30 inches long 
and about f-inch internal di¬ 
ameter. Heat the flask on a 
wire gauze over a burner, as 
shown in Fig. 13, until steam 
just begins to escape from the 
upper end of the tube. The 

heating should be so regulated that the operation will require 
very nearly 2 minutes from the time the heat is applied until 
steam issues from the tube. Remove the flask from the heat 
as soon as the steam escapes from the tube, and rinse the tube 
into the flask in the following manner: Rest the flask, still 
stoppered, on the table and grasp the tube between the thumb 
and the forefinger of the left hand. From a wash bottle in die 
























38 


MANUFACTURE OF CEMENT, PART 2 


right hand direct a stream of cold water down the tube, hold¬ 
ing the latter inclined at an angle of 45°, and rolling the flask 
from side to side on the table, in sweeps of 2 or 3 feet, by 
twirling the tube between the finger and thumb. Unstopper 
the flask, thoroughly rinse off the sides and bottom of the 
stopper into the flask, and wash down the sides of the latter. 
Add a drop or two of phenol-phthalein indicator and run in 
the standard alkali from a burette until the color changes to 
purple red. This color is often obscured until the organic 
matter settles; it is therefore necessary to hold the flask to 
the light and observe the change by glancing across the surface. 
A little practice will enable the operator to carry on the titration 
with accuracy and precision. 

53. If the standard sample contains L per cent, calcium 
carbonate, and d cubic centimeters of alkali is required to pro¬ 
duce the purple-red color, then to find the calcium carbonate 
in other samples, it is simply necessary to subtract the number of 
cubic centimeters of alkali required by these samples from d, 
multiply the difference by 2, and add to L for the percentage of 
calcium carbonate in them; or if the number of cubic centimeters 
is greater than d, subtract d from this number, multiply by 2, 
and subtract from L for the calcium carbonate. 

54. The method described in Art. 39 may also be modified 
and used to check the acid and alkali determinations, as it gives 
very accurate results. To use this method mix .5 gram of the 
raw material with .25 gram of finely ground sodium carbonate 
by stirring with a glass rod. Brush off the rod into the crucible 
and ignite over a Bunsen burner, starting with a low flame and 
gradually raising it until the full heat is attained. Continue 
heating for 5 minutes longer and then ignite over the blast for 
the same length of time. Place the crucible in a 500-cubic-cen¬ 
timeter beaker and decompose the sintered mass in the crucible 
with 40 cubic centimeters dilute (1:3) hydrochloric acid, keeping 
the beaker covered with a watch glass, to avoid loss by effer¬ 
vescence. Heat until the mass is completely dissolved, and 
proceed exactly as in Art. 39 by adding ammonia in slight 
excess, etc. 


MANUFACTURE OF CEMENT, PART 2 


39 


INSPECTION OF CEMENT 

55. It is now the custom to inspect carefully all cement to 
be used in the construction of important government and muni¬ 
cipal works. The large railroads and careful engineers and 
architects also require that the cement they purchase shall be 
tested and meet their specifications. The method of inspec¬ 
tion dififers somewhat with the character and extent of the 
work to be done. Cement is inspected in three ways, as fol¬ 
lows: (1) The usual plan is to take a sample from the car 

as it is received at the warehouse of the contractor, and to 
pile the contents of each car where it can be identified, usually 
in stalls or bins. The sample is then subjected to the usual 
physical tests and the contractor is notified whether or not 
the cement is all right and may be used. (2) The sample of 
cement may also be drawn by the inspector at the mill when 
the car is packed. The sample is then forwarded to the labora¬ 
tory for test. Usually much time can be saved by this method. 
(3) Instead of inspecting the cement in the cars, the cement in 
the bins at the mill may be sampled and tested and the cars 
then packed from the bins containing the cement that has been 
tested and accepted. This plan saves the trouble of storing 
large quantities of cement at the point of use. 

The first method is the one most commonly used, but the least 
satisfactory of the three, as it makes the contractor provide large 
storage sheds for the cement, and, should the latter prove un¬ 
satisfactory, the cement must in some cases be reloaded on the 
cars and shipped back to the mill. The second method has few 
advantages over the first except the saving of time. The third 
method is the best of the three but is suited only to inspecting 
large quantities of cement. If the first method of inspection is 
followed, the testing laboratory is usually located at or near the 
work for which the cement is to be used. If either of the other 
plans is followed the laboratory is located at the cement mill 
when only one brand of cement is being used, or at some central 
and easily accessible point when the cement is purchased of 
several companies. 


40 


MANUFACTURE OF CEMENT, PART 2 


56. Sampling- Bins of Cement. —In sampling cement 
that is stored in bins, the most convenient form of sampler is a 
long piece of 1-inch iron or brass pipe in which slots \ in.X18 in. 
are cut. The edges of the slots should be sharpened, and one 
of them should be turned slightly outward, so that when the 
pipe is revolved in the bin the cement will be scraped into the 
tube. The pipe end is fitted with a sharp, steel point. In 
sampling the cement, the pipe is thrust down to the bottom of 
the bin, using a heavy wooden mallet if necessary, and then 
turned round two or three times in the proper direction to fill it. 
It is then withdrawn, turned upside down, and the cement shaken 
out into a bag by tapping the end of the pipe against the side of 
the bin or running a wire in through the slots. 

57. In inspecting cement tests are usually made to determine 
fineness, initial and final setting time, soundness and tensile 
strength with sand (7 days and 28 days). Chemical analyses 
are also occasionally made to check the percentages of magnesia 
and sulphur trioxide. 


CHEMICAL SUPERVISION OF THE PROCESS OF 
MANUFACTURING PORTLAND CEMENT 

58. The routine work of the chemist at a Portland-cement 
mill is about as follows: 

1. Samples of the raw materials are usually taken in the dry 
process from the mixed drill holes of every blast, and in the wet 
process from every pitful of marl and from every bin of clay. 
These samples are analyzed, sometimes completely and again 
only for calcium carbonate; and, if marl and clay, for the per¬ 
centage of water they contain. The raw materials are then 
mixed in proper proportions according to the results of these 
analyses. 

2. Samples of the dry mixture are taken every few hours 
from the ball mills if these are used to do the grinding, or from 
Griffin mills if they are employed, and the calcium carbonate in 
the samples is rapidly determined. The results of these deter- 



MANUFACTURE OF CEMENT, PART 2 


41 


ruinations are used as a check on the mixture. If the results 
show the mixture to be too high or too low in lime, it is of course 
too late to do anything with the material already ground, and 
the efforts of the chemist must be directed toward making the 
subsequent mixture of proper composition by immediately cor¬ 
recting the proportions of the raw materials. The correction 
necessary can be calculated from the result of the check. In 
some plants using ball and tube mills samples are also taken from 
the tube mills as a further check on the composition of the mix¬ 
ture. In the wet process the slurry is sampled either before or 
after it comes from the tube mills, and if not of correct com¬ 
position clay is stirred in until the mixture contains the proper 
proportion of calcium carbonate. 

3. Samples of the fully ground raw materials are tested for 
fineness on a 100-mesh sieve once a day or oftener, and if not 
ground fine enough the mills are adjusted so that the next lot 
will not be so coarse. Sometimes the product of each mill is 
tested regularly in order better to correct the trouble; and, again, 
only the average sample is tested. If the latter is found to be 
too coarse, however, it is necessary to test each mill in order to 
find out with which one the trouble lies. 

4. The clinker is carefully examined two or three times a 
day to make sure that the burning is done properly. 

5. The ground cement is tested for fineness, setting time, 
soundness, tensile strength (neat and with sand), and chemical 
composition. The mills individually or collectively are tested 
for fineness at least once a day and usually oftener. The cement 
is tested for soundness and setting time at least once a day, but 
it is customary to make tensile-strength tests, chemical analyses, 
etc., of the cement in bins only as they are filled, or, where the 
bins are small, of the cement in a group of two or more bins 
filled consecutively. The cement in such bins or groups of bins 
is also tested for setting time, soundness, and fineness, and a 
statement called a test sheet, giving the results of all these tests, 
is sent out with each car of cement packed from the tested bins. 
When the cement in the bins is unsound it should be seasoned, 
samples being drawn now and then to determine when the free 
lime is all slaked and the cement can be packed. 


42 


MANUFACTURE OF CEMENT, PART 2 


ANALYSIS AND TESTING OF LIME 

59. Methods of Analysis. —Lime is best analyzed by the 
scheme given for cement in Arts. 31 to 38, inclusive. Lime is 
graded by analysis, and the usual classification followed is that 
of the committee of the American Society for Testing Materials, 
as follows: 

(a ) Selected. —Well burned, picked free from ashes, core, 
clinker, or other foreign material. 

( b ) Run-of-Kiln. —Well burned, without selection. 

Quicklime is shipped in two forms: 

(a) Lump Lime. —Kiln size. 

( b ) Pulverized Lime. —Reduced in size to pass a J-inch 
screen. 

Quicklimes are divided according to their chemical composi¬ 
tion into four types: (a) High calcium; (b) calcium; (c) 
magnesium; (d) high magnesium. 

The following chemical limits are used to classify the various 
kinds of lime: 

TABLE III 

CHEMICAL COMPOSITION 



Calcium 

High- 

Calcium 

Magnesian 

High- 

Magnesian 

Se¬ 

lected 

Per 

cent. 

Run- 

of- 

Kiln 

Per 

cent. 

Se¬ 

lected 

Per 

cent. 

Run- 

of- 

Kiln 

Per 

cent. 

Se¬ 

lected 

Per 

cent. 

Run- 

of- 

Kiln 

Per 

cent. 

Se¬ 

lected 

Per 

cent. 

Run- 

of- 

Kiln 

Per 

cent. 

Calcium Oxide. . . 

85-90 

85-90 

90 

90 








(min.) 

(min.) 





Magnesium Oxide 





10-25 

10-25 

25 

25 







(min.) 

(min.) 

Calcium Oxide + 









Magnesium Ox- 









ide. 

90 

85 

90 

85 

90 

85 

90 

85 

Carbon Dioxide 









(max.). 

3 

5 

3 

5 

3 

5 

3 

5 

Silica+Alumina + 









Oxide of Iron 









(max.). 

5 

7.5 

5 

7.5 

5 

7.5 

5 

7.5 


Note. —Hydrated lime takes the same chemical classification as the lime from which 
it was made. 


































MANUFACTURE OF CEMENT, PART 2 


43 


GO. Testing of Lime. —The tests usually applied to lime 
are those for the sand-carrying capacity and for the percentage 
of waste. Hydrated lime is tested for sand-carrying capacity, 
for fineness, and for soundness. 

Quicklime is shipped in bulk and the sample must be taken so 
that it will represent an average of all parts of the shipment 
from top to bottom, and not contain a disproportionate share 
of the top and bottom layers, which are most subject to changes 
due to absorption of carbon dioxide and water from- the air. 
The samples should comprise at least 10 shovelfuls from differ¬ 
ent parts of the shipment. The total sample taken should 
weigh at least 100 pounds and should he crushed to pass a 
1-inch ring, and quartered to provide a 15-pound sample for the 
laboratory. When quicklime is shipped in barrels, at least 3 per 
cent, of the number of barrels are to be sampled. They should 
be taken from various parts of the shipment, dumped, mixed 
and sampled as above. All samples to be sent to the laboratory 
must be immediately transferred to an air-tight container. 

To test the sand-carrying capacity of lime, the latter is first 
slaked to form a thick plastic putty and briquettes are made 
employing varying proportions of this putty (equivalent to a defi¬ 
nite quantity of dry lime) and standard Ottawa sand. The sand 
and putty are thoroughly worked to form a plastic mortar and 
the briquettes are made as described in Arts. 19 to 22, inclusive, 
for cement testing. They are stored in air, not water, and are 
broken at periods after 3 months. 

To find the percentage of waste in quicklime, 5 pounds of 
lime is placed in a box and slaked with sufficient water to produce 
the maximum quantity of lime putty. If too little water is used 
the lime will burn, if too much it will be drowned. The putty 
is allowed to stand for 24 hours and then washed through a 
20-mesh sieve by a stream of water having a moderate pressure. 
No material is to be rubbed through the screens. Not over 3 
per cent, of the weight of the selected quicklime nor 5 per cent, 
of run-of-kiln quicklime should be retained on the sieve. The 
sample of lump lime taken for this test should he crushed to 1 
inch and screened over a J-inch screen and only that portion used 
which remains on this screen, 


44 


MANUFACTURE OF CEMENT, PART 2 


61. Percentage of Available Free Calcium Oxide. 

Lime is much used in the chemical industries and for this pur¬ 
pose it should show a high percentage of free calcium oxide. 
The following is the usual test made to determine this: Weigh 
28 grams of the coarsely ground sample into a liter graduated 
flask containing about 250 cubic centimeters of recently boiled 
distilled water. Boil for 10 minutes, close with a cork contain¬ 
ing a capillary tube 6 inches long and allow it to cool somewhat. 
Make up to the mark and mix well. Immediately after mixing 
draw off 50 cubic centimeters of the milk of lime and titrate at 
once with normal hydrochloric acid, using phenol phthalein 
as an indicator. Allow the flask to remain some time to see 
whether the pink color returns. For the percentage of free 
calcium oxide multiply the number of cubic centimeters re¬ 
quired by 2. 

In the case of hydrated lime use a 1.4-gram sample, place it in 
an Erlenmeyer flask with 250 cubic centimeters of water, and 
titrate the entire volume after boiling and cooling as described. 
In the case of quicklime, the larger weight is necessary in order 
to get a proper average. 

62. Hydrated Lime. —Flydrated lime is packed in bags 
and is sampled just as cement, but the sample should be put in 
an air-tight container. The fineness of hydrated lime is deter¬ 
mined by means of the No. 100 and No. 30 sieves. A good 
hydrate will not leave a residue of over 5 per cent, on a standard 
No. 100 sieve and not over .5 per cent, on a standard No. 30 
sieve. 

To determine soundness, which is due to the thoroughness 
with which the lime has been hydrated, equal parts of hydrated 
lime under test and Portland cement which is known to be 
sound are thoroughly mixed together and gauged with water 
to a paste. Only sufficient water should be used to make the 
mixture workable. From this paste a pat similar to those 
already described in Art. 26 is made, allowed to harden 24 
hours in moist air, and subjected to the steam test. The pat 
must stand the test without popping, checking, cracking, warp¬ 
ing, or disintegrating. 


MANUFACTURE OF CEMENT, PART 2 


45 


ANALYSIS AND TESTS OF PLASTER 

63. The constituents usually determined are silica, insoluble 
iron oxide and alumina, lime magnesia, sulphur trioxide, and 
combined water. The first seven of these are determined as in 
Arts. 31 to 38, inclusive, for cement, the combined water is 
obtained by placing 1 gram of the sample in a covered crucible, 
weighing the whole, and heating in an air bath at a temperature 
from 215° to 230° C. for 1 hour. The crucible is weighed, 
again heated for 15 minutes, and again weighed, and this treat¬ 
ment is repeated until it ceases to lose weight as shown by two 
weighings with intervening heating agreeing to within .2 milli¬ 
gram. Report the difference between the first and last weight 
of the crucible as combined water. 

64. Plaster is usually tested for fineness, setting time and 
tensile strength. The fineness is found by sieving through a 
No. 100 sieve. The setting time is determined with the Vicat 
apparatus. The tensile strength is determined by molding into 
briquettes. The plaster for both the setting-time and tensile- 
strength tests is mixed with just enough water in a pan to make 
a mixture fluid enough to pour and not stiff as in cement testing. 
The plaster is poured into the rings of the Vicat apparatus and 
also into the briquette molds and is not pressed in as is done in 
cement testing. Tests made hv different laboratories rarely 
agree and are consequently only of value when made by the same 
operator, and are hence of use principally for comparing two or 
more plasters. When called upon to test an unknown plaster, 
therefore, procure one which is known to give satisfaction in 
use, and test the two side by side. 








































































